Q: Someone stole my iphone 5. I had the find my iphone app on, and selected to erase the contents of the phone but kept the phone registered within the icloud. Will the person who stole it ever be able to utilize the phone?

No, as long as it is listed in your iCloud account's list of tracked devices, then it is still activation locked.  Nobody will be able to get past the initial activation screen if they try to use it.  You should also report it to your carrier and ask them to blacklist it as well.

Its bad to hear that your iPhone got stolen. If you didn't deleted you iPhone from you iCloud account and set the Device in lost mode then the person how found or stolen the Device won't be able to access to your Device.

I would advise you to inform the Police with the Serial and EMEI number of the Device.

Please read this Apple article explaining your options regarding a stolen phone. The steps you have taken should protect your data:

If your iPhone, iPad, or iPod touch is lost or stolen - Apple Support