What are regulations regarding enlisted-officer interaction on social media?

Personally I don't accept requests nor do I add anyone I work with at the time. After we no longer work together, then I will allow friend requests on social media. If I work with someone or they are in the same unit at the same time, no.

This is a pretty useful bit of material that tries to examine a lot of the hypotheticals. You may be able to find a parallel example to yours. It's a DA PAM, but the examples give answers that cite all the applicable regulations for each scenario.

You're going to get a lot of "I know a guy who knew a guy back in 1987" type comments on this site. Ignore them, stick to the regs, and you'll be better off.

Department of the Army Pamphlet 600-XX
This draft DA Pam contains hypothetical scenarios for training purposes only.

The discussion following each hypothetical is not meant to represent the only correct answer, but to illustrate how relevant personnel should approach issues that may arise under the new Army policy. Readers are invited to submit comments on these hypothetical scenarios and to submit additional scenarios for possible inclusion in the final version of the Pam.
As a draft document, this document is subject to change.

https://www.armyg1.army.mil/hr/command/docs/dap60035.pdf

Most of the fraternization policies relate to those under the same command or being involved with someone who is in your command. I don’t believe this officially violates any policy or procedure, however, the officer needs to look at the etichal dilemma and how the officer would be perceived by his/her peers for being involved with a lower enlisted SM.