Cutting a perfect paint line above vinyl wall cove base (rubber baseboards) is super easy. I've been doing this for years!
NOTE: Yes... you can paint over vinyl wall cove base. I use Benjamin Moore Aura Semi Gloss. It sticks like crazy!
There is a trick to it which I discuss though-out this website.
We don't normally go to this extreme when painting baseboards but this custom built house had so much trim that we completely masked the hardwood flooring off to spray the baseboards and all the trim at the same time.
Preparing for spaying like this was a ton of work but it produced silk smooth results and reduced at least 80 hours labour in comparison to traditional brush and roll.