So can gerbils eat hay?
Yes they can but not as much as rabbits, guinea pigs or chinchillas who need it to grind their teeth.
A handful a week will suffice as anymore will be bad for their tummies. Timothy, alfalfa or meadow is good for them but not more than a handful of hay at a time is good for them.
It’s not a food however that’s worth buying especially for them as there are better foods for them that they will like and enjoy. But if you have a rabbit, guinea pig or chinchilla then yes they could share their hay.