All the advice I'm giving is not necessarily in lockstep with all Marvel policies. I'm trying to give broad info regarding breaking into the industry. The unsolicited pitches policy is something that is in place, but by its very definition can't be totally enforced. Surely at some point, just like in the past, someone at Marvel will see a non-Marvel book they like and solicit some work from that writer/artist. You're unsolicited until you're solicited, if you get what I'm saying.
I'm not totally sure about using Marvel characters in online samples...I assume that's something you shouldn't do. I'd recommend you ask CB Cebulski (he's on Twitter!) about that. He'd know better than me.