I believe pure Mormonism teaches, at the most fundamental level, that salvation and exaltation have nothing to do with religious or denominational affiliation in this life, despite how much we stress the importance of missionary work and earthly conversion. We teach that this life is the most important part of our eternal existence (and I agree with that concept, since "now" is all over which we have any control) and that missionary work is of paramount importance (and I love and am involved actively in that work), but, in the end, all will be held accountable only for how they lived what they believed - meaning good, sincere people of all ages will be blessed equally regardless of whether or not they hear and accept the Gospel of Jesus Christ in this life. Thus, we have an emphasis on the primacy of preaching the Gospel coupled with a theology that says all will be blessed fully and graciously even if we do not do so.
This represents one of the most fundamental paradoxes of Mormonism - the need for specific conversion work now coupled with no eternal consequences on others for not doing that work.
In case anyone disagrees with the universal nature of the grace we teach in the LDS Church, I will try to explain what I mean:
1) "As in Adam ALL die, even so in Christ shall all be made alive." (I Corinthians 5:22)
The Atonement pays for physical death for ALL who ever have lived - no matter what religion they believed in this life and what denomination they attended, if any. This covers atheists and agnostics, as well. "All" means all. Period. Therefore, all are saved from physical death, and all except the Sons of Perdition are redeemed from spiritual death ("Hell" - endless life in the kingdom of Lucifer). This means that all who ever have lived obtain a reward for having lived here on Earth, even those who end up as Sons of Perdition. Everyone except the Sons of Perdition inherit a degree of God's glory in a divine kingdom.
2) Those who die without having had a chance to hear and, more importantly, understand the Gospel will have that opportunity at some point in their eternal existence.
Therefore, even if someone dies without having accepted the Gospel in any obvious way, they can be exalted - if they lived the best they could according to the dictates of their own conscience. Furthermore, there simply is no way to look inside a person's heart and know if that person truly had an opportunity to understand the Gospel fully - which is highlighted by the next point.
3) There will be LDS and non-LDS in all kingdoms of glory.
All modern prophets have said that there will be those who are not LDS in this life who will end up in all the kingdoms of glory, and all modern prophets also have said that there are those who are baptized, active members of the LDS Church in this life who also will end up in all the kingdoms of glory - since where we end up essentially is a result of who we become (what glory we can abide when all is said and done), not who we appear to be to others. It is possible for a baptized, confirmed member to jump off the deep end into wickedness and depravity. In other words, all modern prophets have said that baptism and confirmation alone are no guarantee of exaltation - and, they also have said that even active attendance won't cut it if it's not accompanied by a spiritual conversion.
4) Ultimately, God is the judge of all, since we just don't understand anyone well enough to make final judgments of them.
This means that we really don't know who has had an opportunity to understand the Gospel fully and who hasn't. We often think we do, but we just don't know so many things about others that we can't be their judge. Only God can see into each soul and know the right reward for them. That is important to understand if we really do accept the idea that God is the Judge and that we simply can't make that determination fully and with perfect clarity. I take, "Judge not, that ye be not judged" much more literally than many people do - especially when it comes to assumptions about where others will be when all is said and done.
5) There is no obvious, objective, outwardly-visible criteria (at least to us) that defines who will be where - at least, not on a large scale that can be applied to all.
This is hardest to accept and internalize when it comes to those of whom we have high expectations - especially our own family members (both physically and at church). We generally are hardest on those we think we understand - and we generally are most judgmental toward "our own". However, when it comes right down to it, we simply don't understand anyone well enough to make a perfect judgment about their ultimate, eternal fate.
So, Buddhists, evangelicals, Muslims, Catholics, atheists, agnostics, Mormons, Baptists, wiccans, and just about any other type of person, including inactive LDS and those who have left the LDS Church, can be exalted - as long as they lived the best they could according to the dictates of their own conscience (including doing the best they could to repent to the best of their understanding and ability). That's God's call as the Eternal Judge, not ours as fallen (wo)man - since he can see performance compared to potential, while all we can see is performance (and, really, only public performance, in many cases). We might make value judgments based on our limited understanding of the full picture, but we are commanded not to do so (in too many scriptural passages to begin to list here) - because we are flat-out wrong in too many cases.
I understand fully the issues such a view brings with it, but I believe it passionately.