Do only Odinists and Asatru go to Valhalla?

What about soldiers who died in battle but were of another religion?

Everyone's got their version of the 72 virgins.

I don't think Odin would let a christian into paradise, he's still pissed off at the christian god for having his people killed off by the Romans

This reminds me of Wagner...

Yes, well it must have happened that people of different faiths died on the same battlefield...exceedingly common I'd suggest...and especially ironic if they died over a religious conflict as many would have. As an atheist I don't think any of them went anywhere, but they will never know about it.