But there are a few variables before you decide if you should.
Is the VCT tile well bonded to the floor? Is this an older home? I have seen VCT tiles pop up off the floor fairly easy sliding an ice scraper below them. On the other hand there is the problem of removing the VCT (excluding possible asbestos concerns) and dealing with the cutback residue left on the floor. The cutback has to be dealt with to get thinset to stick to the floor. You would need to scrape as much of the cut back adhesive as possible keeping it wet so as not to release dust in the air. Then skim the floor with ardex or similar and set tile over that. If the cutback adhesive doesn't come completely up but is smooth enough to lay tile over, there are thinsets rated especially to adhere to cutback and there are epoxy thinsets.
My first choice is almost always to remove the existing floor and adhesive to start from the original base to lay my ceramic tile.
If this appears undoable, I would make sure the VCT is securely bonded to the floor and scarify to give a good bond. Then I would use a product such as Durock's tile membrane: http://www.durocktilemembrane.com/
Bottom line is if I'm doing it for someone else, I'd rather go to bare concrete and tile from there. That way I have one less callback issue to worry about