Possibly. Witnesses inform on criminals every day. Retribution is not usually that high on the list of things the criminals have to worry about. I write up crime articles a lot, and most of the time there are multiple witnesses used to build a case before an arrest is made (unless the arrest is made on the spot).
The key issue would be whether Joseph had anything to do with the shooting, such as essentially telling the shooters to do it. It would seem by now that if he did that the shooters would have said something resulting in his arrest, though ... unless, of course, from a cynical standpoint, he's paying them to be quiet about it.
I think the fact that he already has not been charged as an accessory means there's been nothing said to contradict his account. The arrest of the other two happened fairly quickly, so that bodes well for him that police had reasonable cause to believe they were the ones who committed the crime.
If it's capital murder, they will be held without bail until they are tried, which could take up to a couple of years if Texas courts move as slowly as the ones here do. Then, if they are convicted, they won't be out of jail for quite a long time. So unless they get someone on the outside to go after Joseph, then revenge isn't likely ... unless Joseph is hanging out with the shooters' posse and one of them decides to take revenge for them.