Update: I went down the road to the grocery last night and threw a piece of shrimp in before bed. I noticed the crabs immediately went to it and were eating and when I woke up this morning, no sign of shrimp. Tested the water and all levels are 0.
Still apprehensive that I lucked out ... should I try the pure ammonia approach?
You have life i'v the tank, so eventually it will cycle completely. But it would be nice to know if it's safe to add fish, though. I would dose pure ammonia up to 1ppm and see if you can clear it to zero in 24hrs... next if you can clear 2ppm in 24hrs, but start with 1 to see where you are at in the cycle.
Or, you can suspend a shrimp in a mesh bag or pantyhose where the crabs can't get to it...tied to a stick across the top of the tank if you don't have a center brace. But, i like the pure ammonia route best since you know exactly how much you added at a given time.