They certainly might be able to get upgrades that are equivalent in effectiveness, though obviously they wouldn't be [i]exactly[/i] mark V or VI. That would require knowing what eventually goes into them. 

Granted, the Aegis comes from a time when the Gen 2 MJOLNIR for the Spartan-IVs is the norm. What that means I guess depends on how much Dr. O'Connell and Narak know about MJOLNIR and the technologies that comprise it.