Is a different strain.
A lot of (over) bred fishspecies have "developped" their own strain of Iridovirus, but they all have different symptoms and different outcome. DGIV is the most terrible one, but Rams, Angels, Neons etc.... all have "their own".
I still believe the mouthulcers on Neons are caused by it.
Lymphocystis is caused by another.
I wouldn't. The issues with the other fish won't be caused by the actual DGIV and could have had different causes.