hmm.. it could've been something on your evo that HTC added to make it work. They added more security protocols than stock android has, though the xoom supports full device encryption.. so not sure what the holdup is.
Do you know someone in your IT department who you can troubleshoot with? Also, check with the makers of Touchdown and see if they have their app compatible with 3.0 yet.
Sorry, as I don't have a xoom to play with yet, I can't give you any solid answer.