Are the names of companions in SWTOR considered spoilers? You don't find out the info until you reach a specific planet in the story, but you can also see the name of every single one in the Legacy achievements without playing through the story.
In some cases, you encounter someone in the story at a point where it wouldn't make sense for them to become your companion, but a twist at some point makes it happen. You could consider that a spoiler, but it's up to you. I don't think it's nearly severe enough for anyone to complain about it if you don't use the spoiler markup to hide names.