It's very hard to tell from the video. They definitely do not look like hydra to me.
Could it be mosquito larvae? The size seems right, and they do tend to do this wiggly thing when they're disturbed. If you leave them alone for a while, do they float vertically near the surface?
Any other information would be useful. Do you see segments, or eyes, maybe something like a tail or jaw, or do they look more like worms/eels?
---
In general I would say little critters themselves are of no danger to adult axolotls (unless they are parasites, but those wouldn't simply float around). Even if this were hydra, adult axolotls have not much to fear of them.
Sudden critter populations can be symptomatic of something else wrong with the ecosystem of your tank, but in that case it's not the critters you need to worry about but their cause. Have you noticed any sudden changes in water parameters, temperature, etc? Those would be more a threat than the critter explosions they cause.
Other reasons can be more benign. Do you often leave the door or windows of the house open and the aquarium accessible? It could be that some critter happily laid eggs in your water (which I would say is a good sign for your water quality).
Have you recently added unquarantined plants to the aquarium? I had dozens of damselfly larvae for a while because I'm one of those fools who never quarantine plants - the damselfly larvae are harmless (except to other critters - fleas, snails, etc.) and it was pretty fun to see new damselfly hover around the aquarium every so often (also a good sign for water quality, I guess).
Keep us posted!
