Casey/Republican Reef:
Yes, you can have a moray in a 55...just check for smaller species as previously suggested. Lots out there that don't get that big.
A SFE is a little escape artist...but really a charming eel to keep. They're beautiful and easy to care for. Weigh down your tank lid, close even small holes (you'd be amazed what an eel can squeeze through!) and enjoy!
You do not have to feed live fish...in fact, it's ultimately not good for the eel and can get expensive after a while. You shouldn't "feel bad", though. Your eel would be hunting live prey were it still in the ocean, right?!
I feed my SFE rock shrimp (his favorite!), fresh tuna, salmon, squid, and other sorts of frozen ocean fare. I always feed with tongs or a skewer.
If you've never had a moray, an SFE is a great eel to get. They do get fairly long, though...and some eel keepers have seen their SFEs eat their smaller tankmates, so choose his tankmates wisely.