Some of my broms have spikes and no frog has got hurt yet. Although the frogs would see spiny broms in the wild, the risk is still there (especially since you will be sticking your hand in their tank and scaring them). I wouldn't worry about it though.
I'll post the list of all the plants i have in there once i post pics of the tank (any day now!) I ended up not putting the one in the tank because it looked to big for the tank. I'll either put it in my 75 or just pot it and keep it by my window.