I had an earlier generation mini gorilla on a Delta Unisaw and the dust collection was excellent. I think that was a result of the good suction of the MG and also the good design on the Unisaw (shroud around the blade, etc).
I then owned a Hammer K3 and DC was really good while hooked to a Clearvue Cyclone. We moved and I started to sell tools because of reduced shop space. I sold the Clearvue and for a short while had a new mini gorilla hooked up the the Hammer K3.
DC with the MG on the K3 was not a good as what I had with the Unisaw, but I don't think that was because of any lack of suction from the MG. If anything, I think this new generation of MG is better than the one I owned several years ago. The K3 isn't as "closed in" as the Unisaw was, and more dust gets down inside the saw. But with that said, it wasn't terrible and certainly nothing that would prevent me from wanting to buy a Hammer product and to use a MG with it. For the short time that the K3 and MG overlapped in my shop, I just periodically slid open the access panel on the K3 and vacuumed out the dust using my Festool Mini.
I know you're asking about your C3 and I had a K3, but I think the internals are similar and this might give you enough info to apply my results to your situation.
I should say that I also had a vac with a 50 mm hose connected to the blade guard whenever possible, and that helped a bit on the topside with DC.
You have already gotten a good recommendation for contact at Oneida. If that doesn't work out you can ask for my rep and I am sure you will get good advice. I recently bought a MG and Dust Cobra from Mark Schreiber.
I had a couple assembly issues with the new MG. I was able to work my way through them with no problem but if you get one and have any Q's feel free to contact me .
)