It is licenseable. (if thats a word)

Ammo would be your own "problem". Importing from the North is not an issue if you have the appropriate paperwork, but could become a pain to do each time you need ammo. Also as a varmint caliber your ammo allowance on your license may not be large enough to be cost effective from the point of view that if you can buy say 500 - 1000 rounds at a bulk price, but only have 100 - 200 on your license it could be a case of running out of ammo and having to import time and again 100 -200 at a time.

There are a few wildcat calibers already being used so i see no reason why you would not get a license for one, but to address your concern the Gardai would not be too interested in where you get your ammo so long as its done right. Your local FO will get a copy of the import forms from the DoJ each time you import anyway.

A handy tip though. When you buy from a southern dealer your purchase is recorded under your license but with importing its bought/imported through your license, but not necessarily recorded. So make sure you keep records of all amo imports/purchases for renewal of your license. I done this years ago when i first started to import HPS ammo myself. For one year my license showed no record of buying ammo in the south, but i had actually imported over a 1,000 rounds.