Welcome, Aldantefax! Hope you learn much here!
To answer your question, yes, RPG mappers do exist and get paid for their services. Many members here are professional or semi-professional cartographers. If you view the "Map Making Requests" forum, you'll often see requests for bids for pro projects like books, RPGs, publications and individual private games willing to pay for maps.
I've gotten a few mapping jobs from that forum myself. Dog House Rulez, publishers of Sidewinder, recently placed a bid there, which I got after contacting them and created 3 maps for their recent QuickQuests: Eggsellent Opportunity fantasy mini-adventure. So I am in fact a pro now!
I have also created commissioned maps for individual gamemasters - one being used for tournament play at a gaming Con and am currently working on an extended project involving a hundred or so maps and illustrations for a private game and hopeful series of novels based on that world.
Sometimes publication means not getting paid - it depends on the project, who the project is for, a published map you can point out to get paying jobs.
I would think very few cartographers are full time at least in the RPG industry, and outside the GIS mapping world - but some exist. Most of us do something else full time and obtain commission paying map jobs when we can.
I'd go as far as saying that being a member here, participating in the monthly mapping challenges, as well as posting various personal and experimental maps here have been directly related to getting me paid-for RPG cartography work.
If nothing else but to help build a portfolio of work to point to potential publishers of your skill. Consider your membership has a Gallery section in your personal settings. Use this as your mapping portfolio and point potential customers to that link.
Winning a mapping challenge probably helps, though. I'd bet ever single map challenge winner here, could potentially get paid for map-making if they tried.
So Aldantefax, there is hope for you to get commissioned work for RPGs! By joining Cartographers' Guild, you are at the threshold to a RPG cartography career, if you try hard enough!
GP