Might be a good place to ask.
Should not be a problem. Whonix already ships with oxygen-gtk.
I would be careful praising feature abundance. My opinion is that application of high value (password managers, encryption software and so on) should not be an octopussy of functions. The smaller attack surface, the better.
Is there any specific feature that you miss in FPM2?
FPM2 seems to be more up-to-date in Debian repos then KeePassX.
Current release: 2.0 Alpha 5 (December 2013 )
Debian package: 0.4.3 (March 2010)
2.0 is a complete rewrite of the software and 0.4.3 is not longer being maintaned.
Figaro's Password Manager 2
Current release: 0.79 (January 2011)
Debian package: 0.79 (January 2011)