There are no standards to my knowledge for pellet for cooking. There are standards for heating pellets, all of the talk of railroad ties and chemical additives/binders you will not find in pellets for home use, they are for industrial use. Most heating pellets will have a small square (PFI label) somewhere usually close the bottom of the bag that shows the composition of the pellets. Not the actual wood break down but it will show percentage of hardwood and if softwood is used and anything added, usually soybean or vegetable oil for lubing dies if needed.
Many heating pellets today including the brand I have been using for the last few years (AWP) to heat with have a little picture of a grill and says great for pellet grilling or something to that effect. If you find a pellet and want to do some research, most of the companies I have contacted are pretty good with telling you about where their wood is sourced and they will usually tell you if people at the company use them in their grills also if you ask. I have not contacted any companies for a while, I was using Hamers Hot Ones for heat and after talking to them I started using them in my cookers probably 8 years or so ago. What I like about the Hamers is they are short, the buckets I would carry them into the house in to dump in the stove I could get about 2 1/3 buckets to a bag, most others I had used I would get 2 1/2 buckets to a bag. because of them being shorter volume changed like kosher and table salt, also these were primarily red oak.
I have used and still have some lumberjacks, different wood profiles, I can honestly say I cannot tell much difference in flavors when using them vs the hamers.
I kind of laugh at the Food Grade label, I have grown up in the mountains and woods of western PA I have yet to see a food grade forest, I also questioned where the log burner guys find food grade logs for their cooking.
Is there a difference in the pellets from heating to BBQ, probably more than just the cost? Yes, some are labeled as Apple, Cherry or a specific type or blend of wood. Now it comes down to being like anything else in life if you choose to believe what you read on the bag or what they tell you is in the bag then you are good and really that is all we have to go on. Unless we have access to being able to run analysis of the wood make of them.
After 8+ years of using heating pellets primarily for my cooking, I have not dies, grown a third eye or anything like that, so I am pretty good with using them. We are all different in our thought process, so I guess that is where the need for Food Grade terminology comes into play when it comes to pellets.
There is a rural king I stop at when I am close, to it they usually have LJ for around 6 or 7 bucks for a 20# not as good of a deal as $9/40# but not far off if you can not find someone to go in with you on a whole pallet.