I've always found with Velvets that yes, they are low tension and the top of the bass rises, raising the action; but that they also need more room to move, and if you just leave them where they are (or even raise them up more) you may find that you are then able to take full advantage of them. I know that the literature Velvet gives out with their strings (or used to) recommended that people accustomed to steel strings should expect to have a higher action necessary for the strings to sound best.
Of course, some people get hooked on the idea of having some specific string height that's the ideal on their bass no matter what the string, but the truth is that each kind of string will need something different. An action height that would be unplayable with Spirocores (unless you're Drew Gress) is often the perfect thing for Velvets or guts, and if you try to stick with low action on the low tension strings you'll never get the full effect from them.
Just me two cents, based on using all of these strings at one point or another...