A standard condition of probation in Florida is that the probationer is prohibited from possessing, carrying, or owning any firearm unless authorized by the court and consented to by the probation officer. A BB gun does not, in my view, meet the statutory definition of "firearm."
But, if the court orally pronounced at sentencing that the probationer could not possess a 'weapon,' possessing a BB gun may constitute a violation. Look to the judgment and sentence as well as the order of probation.
They sure can try to do that, especially under the circumstances written by the other attorney. Felons cannot have ammunition either. If he does get charged with vop, hire an attorney immediately, as soon after the arrest as possible.