Diagnosed with cataracts and glaucoma. Since glaucoma and diabetes have similar symptoms, should I be checked for diabetes as a precaution?

Doesn't hurt. Most people with glaucoma do not actually have any symptoms, and the link between diabetes and glaucoma is confusing (linked in some studies and not in others). However diabetes is very common and you are over age 40, so a reasonable thing to check just for general health - see your primary doc for advice on this.
Maybe. Cataracts and glaucoma occur more frequently in diabetics than non-diabetics. It would be unusual for your primary care doctor not to find diabetes during a routine checkup. If this has not been done recently, go for it, and mention your diabetes concern to the doctor. A simple blood test can tell you the answer.