But US is not a party to the issue of Russia transferring nuclear technology to India under lease. Russia could do the same with Pakistan and it should be OK.
Ofcourse, US can sanction but it would be unilateral and won't be under the guise of protecting NPT.
Do you know if Russian sailors are present in INS Chakra?
The point is the US opened the door through its own shenanigans and the Russians walked right on through. The US and it’s vassals could hardly kick up a stink about Russia doing essentially what Washington armed twisted the NPT to specifically allow.
Russia could transfer nuclear tech to Pakistan or anyone else, but then the west would impose heavy sanctions on it for breaching the NPT. Not one fart from any of them about the Indian SSN deal though.
As for Russian sailors, I have not heard anything on that, but it seems unlikely, at least this long into the lease. Maybe some would have gone with the boat initially to help train up the Indian crew, but there would be precious little value in India leasing the Akula to gain experience if Russians are still doing all the most technically advance jobs still. Would not rule it out, but would be a ridiculous waste of money if so.
It is likely that the Indians don’t have access to the seal reactor itself, but that stills allows them to operate the boat as normal using standard controls.