Thanks for writing. It's tough to say what's going on without being able to see the plants --- the holes could be from insects or it's just as likely they're from mechanical damage (such as hail).
Rhubarb does best in a spot with full sun, so unless your plant is getting at least 6 hours of direct sun a day, I'd move it to a brighter spot. It'll grow bigger so you get better harvests and in full sun will be more resistant to pests and diseases.
---Justin, Senior Garden Editor, BHG.com