Can answers be submitted by site admins only?

Absolutely not, as you are asked this question without admin permissions :)

I asked if ANSWERS can be limited to admins, not QUESTIONS.

I believe you got the answer for question with your answer.

The answers and questions are being moderated on this site and hence they are not published immediately. You can however choose them published immediately if you wish.

Any user can create questions as well as answers. And it is completely optional and configurable.

Hope this helps.