I don't know how vicious dojo loaches are, personally (or indeed anything about them)... However -- If they're unlikely to attack anything larger than they are, cameroon fan shrimp and vampire (giant african fan) shrimp grow up to 15cm long. The shrimp themselves are pretty much harmless, though they would be vulnerable after moulting.
I don't think smaller shrimp (even amanos) would be a good idea. They'd be pretty much defenceless, and unless they have some pretty impressive hiding places, they might become quite stressed by living in fear so much...
Long arm shrimp would be much better at defending themselves... perhaps too much better. Depending on the species they're often 10-20cm in length and with big claws, they could probably make a meal of a smaller loach. Might be worth looking into though, as there are a vast number of species available.