There is little to no information about iguanas who share their territories. There are probably no animals that can live in harmony with Hulk inside his habitat, even another iguana. On this forum I've read about an iguanas that tried to swallow a Bearded Dragon. It was 1/3 swallowed and the frantic owner couldn't pull it out, so it died. A long time ago I put a wild bird in an iguana habitat. The bird was stunned from flying into a window. In moments it recovered enough to start to flutter around, and my grown ig suddenly jumped way up and grabbed it in a blink. Hmmm, a rainforest tortoise might work, if it's a vegetarian.
Also Hulk will destroy any plant you put in his habitat. There have been lots of discussions here on the topic of how to plant inside an ig's hab. AFIK there no suitable plants. Also igs will eat soil from the plants' pots.