FUNimation will indeed be re-dubbing and re-releasing the first three Dragon Ball Z movies. These movies were originally released in 1997-1998 jointly with Pioneer (whose distribution sub-license has since run out). The voices were handled by the Ocean Group, just as the first two DBZ TV “seasons” were. The English dub’s musical score on these released was actually held over from the original Japanese version.
These re-releases will, just as the “Ultimate Uncut Edition” versions of the first two DBZ TV seasons, feature the English dub work of FUNimation’s own cast. It is very unlikely that they will feature the original Japanese score on the newly-produced English dub audio track.