Well clown loaches are pretty slow growers so unless you are getting 5 to 6" loaches to start id worry about the oscar eating them in a year or so. The problem isnt so much that he may eat them its the fact that the loaches have barbs under their eyes that they will use to stick in his throat and then both are dead. So if the loaches are too big for an oscar to eat once full grown I think it'll be ok. If not no not a good idea. That Oscar will outgrow the loaches by 6 to 7 times at least.