Velocity factor - yes, as stated in the manual, positive values (up to 100) increase the volume according to velocity, negative values (up to -100) decrease volume. Zero is no extra effect either way.
As for Via Vel, I don't understand what you mean, there is no such parameter on Recycle import. If you mean the EXS24 global velocity scaling parameter, then I can assure you it is covered perfectly well in the manual. You'd be best off leaving it to the default, but if this doesn't give you the results you want, then tweak it accordingly.
Where the manual fails to enlighten, experimentation is always a good idea.
This is worth repeating. I never understand the people that post a question along the lines of "I want to do this - should I do A or should I do B" when it would take less time than a forum post to try both and educate yourself as to how to do it. I'm a big believer in self-education - asking others is fine, but it's very good to develop an attitude to help solve your own problems too, rather than always relying on someone else to step in and save the day...