Furthermore, is this the only way for me to ask that question since I don't have enough reputation?
Yes, we can create a tag synonym, and it seems pretty reasonable to me. I'd lean toward making
ess the master tag since that's how people who use it would probably refer to it (and thus search for it), although
emacs-speaks-statistics is more self-informative.
Given the minimal usage of either tag, I've burninated the
emacs-speaks-statistics tag in the meantime.
Re: your second question: currently, you need 1250 rep to propose tag synonyms, so a meta post is one plausible way to draw attention to such a proposal until you get to the rep level (edit: also try suggesting it in chat, as @Faheem Mitha suggests in the comment). You can go that route, but I'd suggest doing so sparingly.