For the reasons Heather (EllasMommie) listed, I really wouldn't put the RETF in there. You're risking disease to the RETF, undue stress, compromised living conditions to make everyone happy, unnatural competition, etc.
As you mentioned, the humidity is also high for GTFs, but I keep mine around there, too, although I caught mine here in Florida where the humidity stays high like that. Now, I forgot what Repti-Bark looks like, but I'd stay clear from anything that could be ingested by the frog, ever.
Anyway, honestly, I'd consider separating the Squirrel treefrog from the Green treefrog, too. One, or even a few, Squirrel treefrogs should live comfortably in a 10-gallon, so it shouldn't be a difficult relocation. The tank is big, so you could even divide it up so the animals don't interfere with eachother without having to find more space. About separating them, the only reason I say this is because of the size differences. My Green treefrogs are nearly twice the length of my Squirrels and will try to attack them. Even if the Squirrel is large enough as to where the Green can't eat it, the Green may still try... it could overpower and kill it, and it doesn't necessarily have to be very hungry to try it. I had a juvenile GTF try to eat an adult Squirrel that was just barely smaller when I tried to introduce them last Winter because the GTF seemed to be interested in the Squirrel's call and I wanted to see what would happen. The same thing happened another time that I tried to feed them together. Well, I've learned my lessons and am just warning you, although it's basically a size thing, because they do live under the same basic conditions. Yours could be used to eachother, but you never know what could happen, so it's a prevention thing.
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Got hips like Cinderella / Must be having a good shame / Talking sweet about nothing / Cookie I think you're Tame 