Seems possible, but if he was using sticky stuff he probably would have been pitching better. He didn't have great control.
However, it's an intriguing thought. And maybe, just maybe, they had a back-up plan where Hendriks would come barreling out of the bullpen with no shirt on screaming, "Crikey it's hot as a shrimp on the barbie out here!" Then he would start hopping around like a kangaroo yelling, "I'm batshit crazy!" In the ensuing madness, the belt could be hidden from the umpires.