Lucky for me I haven't had any problems with my little Otocinclus's.
I keep them well fed. I don't just rely on the algae to feed them, which will actually cause them to starve. I feed them cut up Cucumbers, Yellow Zucchini and green beans. They love this stuff.
They don't get any bigger than 2 inches, so this is why I chose to go with them. They're very afraid of my Axolotls, but not of me lol. I have actually been able to reach my hand in and remove them when cleaning the tank and they didn't fuss or try to flee. They will also nibble on the veggies even when I hold it down in the tank.
The snails are the only thing that work for me getting rid of those pesky Hydra. I also try to keep them well fed on veggies, so they are constantly climbing up the glass, eating the organisms up their way to eat the veggies lol. Right now I don't have a snail in my tank, so my glass is starting to look pretty frosty again lol.
I think it's safe to say that their is always risk involved, but with my schedule, it helps to have little helps such as snails or Otto’s in the tank to keep the pests and algae away
It's really up to the individual. If you feel you need some helpers to keep your tank tidy, just try and make sure that they stay well fed and don't get very big. Frozen pre-cut veggies work, or fresh.
I read somewhere else that a Bristle nosed catfish is ok to keep with Axolotls, but I don't remember where on the forum it is. I also have no idea how big they get either or if it really is safe or not.
Anyone know if these are ok to keep with Axolotls? Personally I like my Otto's