We've talked about the dangers of rented hash many times before. The person who sells you the hash makes money whether their hardware solves blocks or not and if they're a big player they stand to gain by holding back diff from rising. The person who rents the hash assumes all the risk. In the earlier days on this pool the odds seemed to suggest that all the PH sized rentals were suspicious in they never found blocks while the hundreds of TH sized rentals did. I gave people warnings about this at regular intervals. However lately the rate at which PH sized rentals are finding blocks is averaging out to 100% luck so I don't see a problem at the moment, and it could well have been bad luck earlier on. This could change at any time though and there is no way to confirm this. And before you ask if there's a way to check whether rental hash is withholding blocks - no there is no way.
The BEST thing that would be helpful is if the rental service (nicehash, MRR etc) was to report the total shares found by each rental and the number of blocks found by that rental to confirm that it is finding blocks. None of them do that as far as I'm aware.