This is a good question and one with a clear answer in my book. Read on.
I don't hide it and also don't see a conflict of interest here. I think they should be identified as is the default in XF.
That your mods also post a lot of content is unusual, but not harmful, and not necessary for good moderation. It just takes up a lot of their time, that's all and that's fine if they're into it.
IMPORTANT: The fact is that not all mods are the same, because people aren't clones of each other (no edge cases with identical twins etc please!) and thus they will moderate differently and have different likes, dislikes, mood swings and preferences. In short, their human and fallible as all humans are, me included, of course.
This difference is very important, as I've been targeted and bullied by dodgy mods in other forums on more than one occasion, which makes it a horrible experience and one that I've left forums over, permanently. Since they weren't anonymous to me, I could eventually get something done about it on one occasion by speaking with an admin. Crucially, anonymity simply encourages abuse and makes users feel powerless and vulnerable. I don't recommend it.
Thankfully, I have since set up from scratch and run, my own XF forum nowadays, so I'm top dog there and no one can touch me, not even other admins - I'm invincible. Feels good, I tell you. By the same token, I don't abuse my users either as I hate bullying in all its forms and will stamp it out wherever I see it on my forum.