Your frogfish will become food for that eel sooner or later. Depends on the frogfish. I would highly recommend not keeping them together. i hope you have a very large tank for that eel as they usually need public aquarium sized displays or have plans for a home for it when you can no longer keep it. Tim
As Tim said...it'll eventually get eaten.
Or, with your eel only being 12", it depends on the size of the Frogfish...it may eat the eel.
But, either way...no, you can't keep them together.