According to https://cloud.google.com/ml-engine/reference/rest/v1/projects.jobs#Algorithm there are only grid search and random search algorithms available.
According to this blog post https://cloud.google.com/blog/products/gcp/hyperparameter-tuning-cloud-machine-learning-engine-using-bayesian-optimization Bayesian is supported.
So, if supported, how can I tune hyperparameters using Bayesian optimization on Google Cloud ML Engine?