Is it acceptable to use the chabal tetlh for asking more general grammar questions, or grammar questions about existing words, rather than asking about specific words to be translated? If not, is there (or could there be) some resource I could use instead for proposing things to ask MO?
A lot of these questions are things I've asked about or discussed with other Klingonists in the past, but we didn't really come to any conclusion beyond "agree to disagree", because there's not much information one way or another.
Yes. The description on the page reads "Each entry should be a single question or …".
If writing questions about debated topics, I would recommend writing them from an unbiased perspective (IE don't ask "Can I use X to say Y?", ask "How do we say Y?") and then putting the suggested answers so far in either the description or in comments.
Questions of these type may be edited to make them clearer, fix grammatical errors, etc and may be closed if an answer is already known.