Thanks for raising this inquiry. Unfortunately, the RTE does not appear to support vertical alignment options for text at this time. I would encourage either voting for or submitting a new idea in the Ideas for Jive space to help capture this improvement detail for our Products team and the community at large. As you've mentioned, the other option may be by editing the HTML directly, but this is probably not scalable nor optimal for the majority of end-users.
Let me know if you have any other questions.