they have the means to test for kratom. both through screens and labs. i wager that krat0m has not made it onto standard multi-panel screens yet.
only way you will know for sure is when you're called in for your weekly test and you can get a look at the model/type of screening assay. then you can figure out what amount of risk you're willing to take. if they send your stuff in for lab analysis, I'd think that's too risky. they'll find everything they look for with GC-MS.