In that particular situation there are 2 issues, is it something they might test for or detect? and is it a risk for a commercial driver to be taking it? Really the second one is actually more important in terms of not having something happen like hypoglycemia and running into people, or risking harm to passengers by crashing.
To the best of my knowledge, GLP drugs are not considered to be a driving risk, they do not typically cause hypoglycemia, although if the person has diabetes and is on other glucose lowering drugs it could be a problem. And there are rules and regulations about assessing commercial driving risks in diabetes anyway.
Could it be detected in a blood test? I actually do not know, I cannot think of any reason a test would even have been developed, It is not an approved drug yet, GLP's are not even banned in sports, which would be an obvious reason to have a test for it. Maybe a forensic analysis could detect it? Looking for odd spikes on HPLC, but that sort of testing would only ever be done in determining unknown or suspicious causes of death or if people died in an accident, and they were looking extra hard for a drug related cause in the driver, say after noticing suspicious bruising on the lower abdomen that could be due to injections, but it is a bit of a stretch to imagine that actually happening.
Zero possibility of being detected in any kind of routine test. Probably makes driving safer as a lot of people with obesity have sleep apnea , and GLP's improve that, and sleep apnea causes daytime sleepiness which increases accident rates.
Legitimately prescribed tirzepatide would solve the problem, but there is the cost.