I’ve come across the same mixed info, and from what I’ve learned, oats aren’t toxic but they’re not really ideal for guinea pigs either. They’re higher in calories and starch than what piggies are designed to eat, so they don’t fit well into a normal daily diet.
Most people seem to agree they can be used occasionally in very small amounts, mainly for pigs that need to gain weight after illness.
But for healthy piggies, hay should always be the main focus, with fresh veggies and a good pellet.
A lot of store treats include fillers like oats, so
website I usually just skip those altogether and stick to more natural options.