Google's documentation says that when we create a dataproc cluster it uses projects default service account.
source: https://cloud.google.com/sdk/gcloud/reference/beta/dataproc/clusters/create
Is it possible to use some other service account other than default one?
Not possible at this time. You may also want to take care; you're looking at the docs for the gcloud beta dataproc command. If that is what you want then no big deal, but if you're just using gcloud dataproc then these docs will be more helpful.