No. You can't use a network specific ROM on a non branded device (or vice versa). I know whey you're mentioning the T-Mobile ROM, the WM6 update for the Excalibur first came out on the T-Mobile branded MDA unit and as a result there seem to be a lot of copies of it floating around online in various forums.
Do yourself a favour and download the correct version from the HTC website. It's totally free and all you have to do is register with the HTC e-Club; here's a link to it:
http://member.htc.com/member/login.aspx