If the flange is made to bolt in the cats place then it will fit. I don't think pressure will cause a problem as cats are very restrictive so in theory that would build pressure as the gas try's to escape through it. And that would more than likely cause a blow with hot gas trying to escape where it can, but that doesn't cause a blow. So you'll be ok I reckon . Just make sure the de cat pipe is the same diameter as your exhaust.
I will say that make sure you fit flanges on straights and not on bends. I had a full stainless made that had de-cat and it had a joint on the down pipe bend that was forever blowing gaskets it soon got sorted after an argument