I'll admit, as much as I am annoyed about how much spotlight Swampert gets on the site (Not the user, but the Pokemon :P), Swampert would work in perfect synergy with almost every Pokemon on your team.
Swampert can Earthquake without hitting Charizard, and can hit slow with Avalanche, while Charizard hits fast with anything! Swampert, frankly, would clash with others, like Metagross and Tyranitar, but you wouldn't be double-battling everytime.
Swampert and Garchomp would both have STAB Earthquake, resulting in a very powerful OU team. The mixed coverage against many types would also help out your teams small weaknesses.
My only issue with Swampert in this team, is that you'd then, have a whole team of Physical attackers, with the exception of (Possibly) Charizard. Snorlax would be your only means of sponging Special Attacks, and if you come across a strong Special - based team, you're in for a close fight, and if not, a loss.
It's really up to you, though. If you feel that there's more upside to Swampert than downside (based on your team), then I'm not obligated to stopping you. :P