Just me but I wouldn't put an eel in with smaller reef fish. IMHO they belong in predator tanks.
Anyways for FOWLR there are some pretty cool options.
Any of the Pygmy or Dwarf Angels should work (although stick to just one)
The Pearlscale butterflyfish is nice but if I had a 75 gallon FOWLR the Spotband Butterflyfish aka Dot and Dash Butterflyfish would be number 1 on my list. By far the most colorful butterflyfish that would work in that size tank
Wrasses, any of the Flasher, Fairy or Peaceful Halicheres Wrasses would be great choices (although be aware that Halichoeres require a sand bed)
Marine Betta
There are many others (ie Gobies, Dartfish, Blennies) that could work in a 75 gallon FOWLR. My recommendation is to spend some time at www.liveaquaria.com and see what you like. They are pretty accurate for recommended minimum tank sizes, level of care required for a given fish and temperament.
Wrong! All I have in my tank are small fish with my eel. He hasn't bothered a fish yet and I've had him for 4 years. Don't feed them fish and feed them when hungry and they are model citizens. My mandarin lives in the same cave as him . He visits my diamond gobie's home on occasion. He's the main attraction in my tank.