Oof, really depends on the decorations, the axolotl, and whether or not you want to feed the shrimp.
If you do not have any decorations or hiding places, the axolotl likely won't just "eat some", but eat them all. The axolotl will be fat and happy but you won't have any shrimp.
With hiding places, it depends on the axolotl. Some axolotls are idiots and the shrimp might survive; others will be cunning hunters and will eat the shrimp regardless.
Hunter-prey relationships aside, how many shrimp fit in an aquarium depends less on the size of the tank, and more on the amount of food. Shrimp don't really need personal space - as long as there is enough food they'll be happy to live in an "overcrowded" tank.
So, basically, how many shrimp a tank can handle depends on whether or not you want to feed the shrimp, what kind of food you give the axolotl, and if you have any other sources of shrimp food (like decaying plants).