For example, can I just take VectorLinux, change a bunch of stuff, then make a new release?
Yes, of course you can, but you couldn't call it Vector Linux. That's true of any Linux distribution licensed under the GPL or any similar Open Source license including so-called commercial distributions.
There is a business called Vector Linux. Whether or not it actually pays the bills for Robert (Vector), Darrell, or anyone else or not I honestly don't know. My guess would be not.
I can point to packages I've built and even one little bit of code I've written that ended up included on VL 5.9, 5.9.1, and 6.0 isos. I do a lot of the repository maintenance at the moment. I am a volunteer and I do not get paid a dime. How much I do depends on how much time I have, what else is going on in my life and how motivated I feel. A lot of community volunteer work by a lot of different people goes into Vector Linux. Robert and other core developers make the actual decisions.