A: Stephen’s answer: I believe this is a state law you are asking about.
There are many instances where the criminal laws employ “presumption” in the employ of crafting the statute. A presumption is where you accept a fact as true without any supporting evidence.
For all criminal charges, you are innocent until proven guilty, even in cases where the law applies a presumption of some kind. In a homicide, you may be charged with murder even though you claim self-defense; you must assert self defense at trial. If you are charged with drug possession it is presumed you know what the drugs are and that they are illegal; if otherwise the defendant must assert those facts. In this way, the law is crafted so that a defendant exposed to a presumption has every right and opportunity to overcome the presumption if tried for the crime.
SO, if you were arrested for a crime and charged with having a scanner in your vehicle as well, it means the police do not need to witness the act of your using it to assist in the commission of the alleged crime, that much may be presumed, and be, by statute, probable cause and they may charge you with that. However, it would still have to be proven at trial and you could assert in your defense any fact that tends to destroy the presumption.
Such a presumption could possibly allow the defense to ask for additional discovery, or to challenge the constitutionality of the statute’s use of the presumption, or otherwise make this companion charge much more trouble than it is worth. Therefore, in practice, such a charge is perfect as being offered to drop in exchange for a plea of guilt on the companion, and likely more serious, charged offfense.
Each case is different, and this is why you would require a defense lawyer to assist in an actual arrest.

A: Stephen’s answer: As far as the state of Florida is concerned, you were not convicted of a felony because adjudication was withheld, meaning you can buy and legally possess a firearm in Florida. You posted this as a federal question, however so here are some considerations as to federal law. Be generally advised that for the purposes of sentencing scoring and some enhancements to federal law violations involving a firearm, the withhold of adjudication does not factor into the equation and you are considered a felon for that specific purpose. Also, federal law enforcement folks, and those from other states, may not know what a withhold of adjudication means, see the listed felony charges and plea/disposition, and make an arrest which you would then have to defend against. So be careful on federal lands and other locations where the feds might exercise jurisdiction.

A: Stephen’s answer: It is up to the PO to use discretion to formally violate you or not. If formally violated, it’s likely a no-bond capitals will issue, meaning jail until court, at least. Once the violation itself is served, the outcome ultimately depends on the judge. Consult an attorney, as you may have defenses and representation can result in reduced risk of arrest, a long jail wait, and then may make the best of any outcome on your behalf. Good luck.