Ignoring the metabolites making this physically impossible, this is highly unlikely on the face of it.
You mean to tell me the cops were handling loose cocaine - not packets? - in gloves and forgot to take off the gloves after completing evidence recovery. The same cop that completes the evidence recovery then, still wearing gloves, made physical contact with one of the children and specifically touched her hair.
Nevermind the cops went in there expecting to find cocaine, expecting there to be kids in the house, and it is likely that they would have planned to separate the kids - using CPS, Sweep was present at this point right? - and recover evidence. Nothing they found was unexpected, and this would have been routine work for them.
None of that would be impossible, but again this would be the result of terrible planning that we haven't seen at all this far from the police or CPS in this case.
Then the section of hair they touched just so happens to be the hair recovered by Minnesota Monitoring for the recovery of the hair? Was this the same day - I thought it happened after the fact, the kids would have been showered and changed... Again, not necessarily impossible, but incredibly unlikely.
Then you add in metabolites, anti-contamination protocols... If this is true that he said this to EVS, Nick is outright lying. I believe EVS though, as it corroborates Ralphs belief that the hair test would be "thrown out", but I'm not even sure it can be "thrown out" of the CPS case - it may impact sentencing decisions in the criminal case, but it's immaterial as to the charges. The hair test is highly embarrassing for Nick, but I don't really think it matters legally for him anymore.