Well in terms of micro fauna there's a huge range of possibility for what it could be: particular type of algae, possibly a fungus, or maybe some sort of slime mold, amongst others. I don't think it would be necessarily harmful. The fact it showed up in the quarantine tank is not surprising, as the new animals could be harboring microbes. If you've bought any new plants and put them in, then that is a more likely vector of whatever it is. If there are no plants in the container, then it's probably a good idea to really make sure the quarantined animals are healthy before you introduce them to the normal tank; or to do a complete tank overhaul, possibly with bleaching as well, and then see if the organisms come back, this will tell you whether or not the new arrivals still have the potential to carry the strange organisms. My guess is what ever it is, even though possibly carried by your new animals is unlikely to be infectious or harmful, but I could be wrong; though from what you say it seems like it's a nuisance to your cleaning. How quickly do they grow back?
If you do determine that the axolotls are the cause, a salt bath might be a good idea, but if they seem to be healthy, and the organisms don't grow back after overhauling the tank, then I think that would be overkill. Just salt bathing the axolotls and drying out the tank might not work as many of these organisms are capable of making drought resistant spores that could cling to the glass, float through the air, or remain on the filter, glass or substrate unless rinsed thoroughly or bleached.
Also, I know that your camera might not be capable of capturing a photo, but taking a picture, even a slightly blurry picture would help. Also if your camera doesn't focus small enough, I'd recommend taking a larger, high resolution shot of the glass as close as you can get (for maximal detail), then cropping the picture so that it just includes one or a cluster of what your talking about. Then maybe some of the microbiology buffs will be able to pinpoint it for you.
Finally, does it show up in well lit or shaded areas? Have you seen any types of planarian in your tank? To see what a planarian is, go to
http://en.wikipedia.org/wiki/Planarian, I've had them in my tanks before, they seem pretty harmless, I have a feeling you might be seeing the eggs or larvae of these guys. They range in size from barely visible, to about 2 cm long, can be all sorts of colors, and might not be immediately obvious because they often hide, can be very slow moving, and flatten their bodies out into strange shapes. Have you seen any types of small animal in your tank? Isolating one of the clumps and giving it a few weeks to develop might also answer a few questions.
Axolotl Enthusiast