Currently, we are working on the RNN support for hls4ml. So, we do not have the finalized version of the code yet. The branch you pointed out is an old one. More updated code could be found in one of our forks:
Github - https://github.com/chaitanyaPaikara/hls4ml/tree/keras-rnn
Can you please try it out? The implementation in this fork should be able to successfully convert TensorFlow models to hls models. It works mostly fine for small RNN (LSTM and GRU) models. We are still in the process of creating a finalized version and add the RNN support to the official tool.
Regrading PyTorch support: Until now we have not tested/explored the PyTorch implementations in the context of RNN layers. We have been working with TensorFlow models. So, PyTorch models are not supported yet.