Well - just my two cents. The title feels inaccurate. You all are tuning hyper parameters with respect to the performance of the classification task. The bayesian optimization is really to optimize the unsupervised -> supervised pipeline. I was expecting some bayesian optimization of strictly unsupervised representation learning (ex. we have an autoencoder and use some bayesian optimization to tune hyper parameters in order to minimize a reconstruction error). This is really just supervised learning with even less supervision (which is quite typical).