Hmmmmmmmmmm ................... I don't suppose you know more about this MS rod?
If you know there is high Ni - how much? Are there any other elements present? Molybdenum, Chromium, ...........?
Take for example the case IF your MS rod is AISI 4340 - it can be welded, however, you need to follow proper preheat and post weld heat treatment. And it should only be performed on 4340 that has been annealed or normalized.
So please tell as EVERYTHING you know about this MS rod.