There are videos here of panels from AnimeFest with a few voice actors from the FMA dub. Caitlin Glass (Winry) is in the most recent one, and at one point she talks about how she had trouble crying in the first scene of episode 3, and she sings a song from Spiral too!
So far, just from listening to her talk, I think she'd do an okay job. It would be funny if she sang the dubbed version of Motherland. ^_^
(Additionally, Vic sounds like he really loves FMA. I mean, he had a gooshy voice and everything.)