You may only join 1 team. Also, all team slots are taken by mine, graginar (sorry if I spelt it wrong) and X-Scissor. The teams thus are:
Guildgrouper (by mwah),
Maelstorm (by X-Scissor), and
Frostharvest (by jragonair)
You can join other user's Rescue Squad (given though the fact the humans came to fix the calamities and rescue Pokémon), but there are 2 UPG (Users Per Group). Maelstorm has been taken up.
Shadow Mist, your group will be the 'bad group',the humans seeking vengance, like Team Meanies or Team Skull. Unlike the other 3, you will control all 3 'Squadies'. Just post if you like the idea (I recall you saying in your sig that vengenace is...something...um...)