No, agents are not required to offer Alternatives to Revocation. Agents go through what's called a "Plotkin analysis" (named after the Plotkin case in Wisconsin) that looks at the needs and likelihood of controlling the behavior, correcting the behavior, and not depreciating the seriousness of the violation. They then need to discuss all alternatives considered and explain their rejection, including amendment of his Rules of Community Supervision, Placement in an alternative group home (i.e., a halfway house), Electronic Monitoring, any institutional and community ATRs, and simple warnings.
Having an attorney can help negotiate an ATR, but if he was picked up on a felony -- particularly a Felon In Possession of a Firearm, which implies that he had a past felony in the first place -- after only a year on probation I'd say it's highly unlikely he's going to get an ATR. Not to put too fine a point on it, but unless he can show the gun wasn't his it's going to be pretty hard to justify an ATR by arguing something like "I didn't realize having a gun as a felon would be a violation."