There are synthetic cannabinoids that are listed as controlled substances, however, in order to know for sure if what your son possessed was illegal, according to the schedules, a lawyer would need to see the lab report from the actual test if the substance.
Instead of posting questions and answers on a public site concerning your Son's activities, it is best that he retain an experienced criminal defense attorney. The attorney will be able to investigate all the facts and circumstances concerning the case. Good luck.
XLR-11 is not a scheduled controlled substance as of yet, but that is not the same thing as saying that it is legal. It's a substitute for cannabis and likely a designer drug under Section 13 (a) 36 of the Drug Act. Depending upon the appearance and use of the finished product in which it was incorporated it might also support a charge as a look alike drug under 13 (a) 35. He needs to be in contact with a qualified criminal defense attorney who is experienced in the handling of drug cases without delay, and no further details should be posted on the Internet.
Even if substance was not illegal in 2012, your son may have violated the terms of his parole. A standard parole condition is that the defendant remain sober. For example, alcohol is a perfectly legal drug for those over the age of 21, however, those on parole are not permitted to imbibe. If your son has not done so already, he should consult with an attorney about this situation immediately.