Okay, here's a question too- I was thinking along the same lines myself. What if you wanted to use well known characters, but NOT as cameos, but as subjects of maybe scrutiny or even humor? The only money being made would be the possibility of being supported on the site, rather selling said comic.
For example, let's say I wanted Sonic The Hedgehog to have a conversation with one of the characters in the comic about something related to the games or the comics or what have you. Or, let's say I wanted Kurosaki Ichigo to interact with a character. Let's say I wanted Ryu from Street Fighter to make an appearance, or Samus Aran to vouch for women in video games, or Spider-man to preach about responsibility and crack a few dumb jokes, or hell- even use the likeness of youtubers, not for the sake of views or popularity but to ACTUALLY craft the episode around the pivotal point of whatever the character had to offer.
How does one approach this? Is it cool to just throw 'em in there, or is this taboo? Are there red tripwires to crawl around? Money to be paid? How do you even credit that in a comic? I feel like the answer could be simple, or it could be hella complicated and I don't want to bother anyways. I totally understand asking creators for using their characters, it's easy to come into contact with people on the site here. But what about corporations? Do they even care about comics on tapastic?