Can eucalyptus oil be put in a vicks vaporizer to help with sinus issues?

OK, but clean well: You probably can use eucalyptus oil. If you do, make sure that you thoroughly wash it out after use. Vaporizers can get plugged up. Another alternative is to use water with a pinch of salt as an alternative to their proprietary products

Depends: These agents can either help, or act as an irritant and trigger swelling and drainage. Your response could go either way. I never use any such materials for pre-school kids, their airways are not as tolerant to the irritating effect as adults.