Fittings are screw and nut type and will seal well to the fabric, with perhaps a little glue or a rubber gasket. I’ve used those for attaching inflation tubes. Problem is more likely between fitting and crossbraces as it’s not easy to find exactly matching sizes. And perhaps if your fabric is on the thin and flexible side then the hole in the fabric could stretch and come out of the fitting. For Extremtextil 450g nylon I would trust it while for thinner fabrics some reinforcements could be useful.
But yes, making more holes in airtight hulls is not exactly the safest bet.