Products that do not contain THC can also produce positive results in drug tests (only in the form of urine and saliva tests). However, this is extremely unusual. If a test, against all odds, should produce positive results, it only shows that a form of hemp cannabinoid exists in your body.
If you take THC-free hemp oil and require blood tests (only urine and/or saliva samples), then the blood test will show which cannabinoid was detected. In this case, it will show more cannabinoids such as CBG, CBC, CBD and CBN but no THC. This is perfectly legal, and you go free.