LDS believe that the dead have the opportunity to accept or reject the ordinances performed on their behalf. They don't know if they have (though there are individual stories of someone appearing to someone, or hearing a voice, confirming the acceptance of the ordinance).
They offer all of the ordinances performed for the living for the dead as well. When I was LDS I participated in proxy baptisms, confirmations (both as a proxy and administering these two ordinances to others), priesthood ordination, Initiatory (washing, anointing, clothing/authorization to wear the garment, new name), Endowments, and sealings. Some of my LDS friends told me how people (generally in Utah and other areas with tons of LDS) would go on dates to the temple, even to do proxy sealings. I always thought those were awkward. Like, we would try not to look into each others' eyes while we were getting eternally married on behalf of others. I did like being in the sealing rooms though, and thought doing the sealing of children to their parents was nice.
...but then, it was all false, however nice it was.