They can get impacted with anything loose, doesn't matter if it's Fluker's fake moss or real expensive top of the line sphagnum moss. Each gecko is different and you have to watch them closely to be sure they're not trying to lick moisture from the moss and ingesting it at the same time. I have been through this before.
I think REAL sphagnum moss works much better than flukers anyway. It holds moisture for much longer than fake moss or paper towels.
The only loose substance I ever have with my geckos is a a container filled with eco earth. And that is only for the prego females. I have never had a problem with the eco earth though
If you want moss in there, try putting it in their moist/humid hides I have coco fiber/eco earth in mine, and all my geckos love it. never had a problem with them eating it they love digging and making "nests" along the walls of the hides