poweramp is a good player. But to answer your question yes the stock player will play most formats such as mp3, aac, ogg, wma. These are ones that I have used so far.
I've had the best results with ogg.
The first time I put music on my X I used Motorola's software. It launched Windows Media Player and synced my selections there. It took an incredibly long time because first it reformatted everything to WMA and WMV. Because of that (and the fact that my music played fine) I'd have to say yes, the X should play your WMA files without any problems.