Dear lin, xiaobo,
OpenVino is primarily a Computer Vision (CNN) tool. However some aspects of RNN such as LSTM and GRU (used by NLP applications) are definitely supported.
The train.* error you are getting though makes me think that you are not freezing the BERT Tensorflow model before feeding it to OpenVino Model Optimizer. If the model is properly frozen, then you will not see errors related to training. Please review Freezing Tensorflow Models for more information about freezing a Tensorflow model.
Hope it helps,