We have multiple EGCs all the time. Every time you pull a green wire in a pipe you have a parallel EGC and the HCF rules even require it.
As far as the code is concerned ground is ground and the more the better. If we have multiple circuits passing through a J box, don't we bond all of the EGCs together? We reground the EGC pretty much any time we can (generator frames, additional buildings etc).
We do get concerned with the neutral.
