Hi, as the title says, can you do that? Put Cotterless cranks on ISIS hub?
I got 114mm cranks that are cotterless
On my current unicycle, I got 100mm cranks that are ISIS (a qu-ax profi)
No you can’t, just take a look at the spindle and you’ll see why.
You can’t put a square peg in a splined hole.
Or vice versa. 
Even IF the diameter of a splined crank is smaller (or equal) to the smallest diameter of a ISIS hub, then the costs to CNC your crank will be a little fortune (good to buy multiple top unicycles).
So the other option is to drill the cotterless-hole to isis-hub diameter, and weld it on the hub. Even if you succeed in getting that all perfectly straight, then it’s difficult to ever replace a bearing or spokes.
So reasonable speaking, none of the above would be any practical, so the answer is a plain “no”.
A competition for stupid ideas
It should be do able to drill out an aluminum square crank with a tapered drill to more or less match the taper of the hardened steel splines of an ISIS hub. Then just beat the crank on with a correctly sized mallet and bolt it up. Wa lah .
You get bonus points if you live in Russia and this actually saves you $.