They did not have to pull a grounding conductor at all, the IMC is a suitable grounding conductor.
Once they decided to run or the job specifications required a grounding conductor it must be installed per code.
Table 250.122 requires a 3/0 cu for a 1200 amp OCPD and 250.122(F)(1) requires that size EGC in each raceway.
As far as the bonding bushing they may have been used just as the insulating bushing required by 300.4(F). Depending on the installation bonding bushings may not be needed.
If these are feeders and the IMC is not entering the enclosure through concentric KOs bonding is not required by NEC.
Bob
