Traeger Grills product is well known to beetle enthusiasts in the United States ONLY because they are the original producer of the wood pellets, and we had no other brands available LONG TIME AGO. I've used many different brands of wood pellets simply to save some money. I produce more than just couple bags of substrate each year. I saved A LOT of money from not purchasing the TrageraGrilll pellets.
However, depending on the brand, the size of each particle may differ. They work fine. BECAUSE they are same species of wood (if you buy white oak from TG and white oak from other brand, then obviously yea. they are white oaks). If you have cheaper brand easily acquirable, go ahead and use it! I've used multiple different brands as well as different wood types. Hardwood mix works fine, hickory didn't work quite well, mesquite is okay, if you do well job on fermentation (fermentation of mesquite seems quite challenging, but is good food for larvae if well done).