Hej,
I've never had Rostyles, but I've had other car's with split rims and never had a problem. Although one thing to bear in mind is if the wheels have been chemically dipped to refurbish them the chemical used can erode any sealing compound originally used. There was a product we used I think it was called rimseal(?) That helped the tyre up onto the bead and sealed any imperfections in the rim. It's used for motorcycle tyres mainly, short of rebuilding them I think there's only one surefire way of finding out if they're airtight or not. Hopefully someone else can point you right on this.