Can HMM be used as a binary classifier?
I have no experience in hmmlearn. 

But if you want to receive the labels for the underlying states of the process you have to do 'decoding' by using the 'Viterbi' algorithm. It calculates the most probable state sequence for your data. So if you only have two hidden states it calculates a 0/1 label for each of your time-stamps.

If instead you're trying to discern between two different processes and recognize them, you have to train two different HMMs for the two processes and calculate the foward probabilty up to time t. Then you can choose the process with the higher probability.