Any wood in contact with soil can be attractive to termites. It's unusual for them to infest mulch, but it can happen. Instead, termites are more likely to attack decaying stumps or fallen limbs that contain large pieces of dead wood. As long as you keep the wood-based mulch a foot or so away from the house's foundation, you should be able to see any mud tunnels that termites would make as they cross the barren zone. Also, bark mulch contains few wood fibers, so it is even less attractive to termites than are wood chips. You might consider using pea gravel or crushed stone next to the foundation, and wood chips in the landscape farther away from the house.