Does anyone know what wood this is? And if it's safe for gliders?

That looks like what I get at Petco, I've been using them for at least a year now, maybe a bit longer.

I've purchased several over time. I have some that don't have full bark on one side, and some that look exactly like that one. I clean them weekly or biweekly even. I spray them down with v/w solution, let it sit a while, then at some point during the week, I'll soak them in soapy water (I use orange scented ajax, but you can use any dish detergent, I believe). Rinse very, very well, and then let set to dry, usually about a week before I put it back in the cage. This is why I purchased several, so they have time to get cleaned and dried prior. The hardware (screws) do get a little rusty, but they're outside the cage, my gliders have never had contact with that portion.