Has anyone ever successfully quit a hard drug and PMO at the same time?

I would say go for it.

Quitting one hard drug can give you the energy and willpower to also quit PMO.

One addiction is the gateway to another addiction

 

It's really hard to say, as there are way too many variables, depending on personal brain chemistry, the drugs in question the severity of both addictions, the social environment, etc...
That said I've managed to quit smoking after 13 years while having psychotic breakdowns and staying away from porn and cannabis as it was my way of telling my brain that I'm still hopeful for the future. Wasn't really easy but in the end neither porn nor smoking would've made the situation any better.

But if that we're for example a serious alcohol addiction instead of cigarettes and weed It would've been another story i guess.