Katy, you're correct in that if there had been other arrests they would be known - if people are paying attention. I'm sure Ago knows the names of the convoy members from his client.
All arrestees who have been held have to be presented before a judicial officer in court within 48 hours. The case is papered by the USAO and the charges start through the system or no papered (dismissed). There are some arrested on misdemeanors and/or traffic charges released at the precinct to return to court from anywhere from 2 to 4 weeks later. At this date I don't see this applying to the convoy.
If a co-defendant had been arested then it would be public. We don't have secret arrests. Of course, I don't know all their names but others must know.
If a member of Wint's convoy had been arrested or charged then we'd also know that. For them, I suspect either they convinced the USAO they were assisting in Wint's surrender or they are cooperating enough that no charges are being considered or any charges will be dealt with at a later time. If any of them were subpoened to the grand jury then they would have been appointed attorneys for 5th Amendment purposes even if no charges are contemplated. If charges are contemplated then the 5th Am. atty would be working on that in conjunction with their testimony - if they do testify. The USAO is not going to reveal its witnesses until it has to.