As with most things in reefing there are no hard and fast rules. My lawnmower blenny and Tomini tang have been together for close to 3 years now and get along fine.
I will agree that the blenny's algae eating is overrated. He eats the film on the glass and rocks and that's it as far as algae control goes. The only other thing he eats is pellets and although I'm not a big fan of pellets they are in the food rotation to keep the blenny happy.