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.
You don't normally go to this extreme painting baseboards but this custom built house on Eagle Mountain Homes in Abbotsford, BC, had so much trim in it that I completely masked the hardwood flooring off to spray the baseeboards and all the other 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.
Below is a picture of me taping off the boaseboards.