Shit dude sorry for the late reply. I'm afraid I have never used the vsynth but i think it should be able to map time to a modulation source. As far as I'm aware the sampling portion of the synth was designed to use the variphrase engine in a synth like context; I know you can use the screen to modulate the time specifically so its not much of a stretch to assume its assignable to other things. You should at least check the manual or just go play with one :D
The vp9k is much more "phrase sampler" approach and it doesn't really have much of a synth engine to speak of (no filters, lfos, envelopes, etc.) but you can use midi or just twist the front panel knob labelled simply "time" which also sends midi on any cc number you like.
Was reading this thread about Roland VP9000 and V-synth, you mention the fact that ableton/acid cannot do timestretch modulations like VP9000. Do you happen to know if the V-synth have them? It seems the same technology but I am not sure cos.. corner cutting and other factors.. Any info appreciated!