If the vehicles you are referring to are the ones you call from GSX, then no, GSX will only use its own vehicles.
About Living World vehicles and/or vehicles when using the default Ground services, you can't mix and match between two products. If a product defined a Pushback in a region, and another product defined a Pushback in the same region, the vehicles for that particular type will only come from one product, the one getting an higher priority in the sim, in alphabetical order, but with the ones in Community getting an higher priority over the ones in Official.
You might *try* to move the Simultech package in the Community folder, and perhaps it will get an higher priority than GSX world-of-jetways, but then you'll have all Simultech vehicles. For AI and default Ground services. Full GSX services are completely unaffected by this.