Well that's a hard question to answer. You say you don't tend to enjoy single player games. Is there any chance you would enjoy them if the game happened to be outstanding?
Because that's what Skyrim is. Its an absolutely outstanding single player experience. Its a game that gives you immense amounts of freedom to play the way you want to play in a vibrant, rich, living/breathing world with some of the most interesting fantasy lore ever made (be it books, movies, or games.)
I think playing Morrowind, Oblivion, and Skyrim could probably add to your enjoyment of ESO. You'll probably understand the context of the world more and it will add to your immersion. Is it needed to enjoy ESO? Hopefully/probably not if the developers do a good job with the game.
I would say if you decide not to play the games then you could at least read up on some of the lore, watch some videos, and learn some generally things about the world and what has happened in other games. UESP.net is a great site for this. They have summaries of all the quests as well as summary articles on all the topics. You can go there to learn about the setting of the game, the gods, the general history, and much more.
I'd suggest reading through the http://www.gamesas.com/topic/15282-elder-scrolls-lore-faq/. Its really short (won't take up too much of your time), its well written and well organized, and it'll give you a baseline of knowledge that you should probably know to get the most out of ESO. If you start finding that you really like the stuff or if you just want to learn a little bit more, check out the http://www.gamesas.com/topic/1112211-how-to-become-a-lore-buff/ thread. Again, its broken down by subject so you can learn about what you're interested in and ignore other things.