Hi Rare,
A good proportion of the population have H.Pylori, while POIS is very rare, so I doubt that H.Pylori could be a direct cause of POIS. But in someone prone to POIS ( we don't know yet exaclty why!), if this bacteria causes stomach problems, I believe it is a good idea to manage it, since any source of inflammation in the gut should be avoided, be it from irritating food, gluten, a bacteria, a bad gut flora, dairies, or anything else.
I think the lower we keep our chronic, "baseline" inflammation level, the less severe our POIS symptoms are.