Retina surgeons are rarely brilliant cataract surgeons. I would not want a retina surgeon doing my cataract surgery. If the cataract is preventing the retina surgeon from having a very crisp view of the macula, the cataract surgery must go first. It may worsen the pucker, but that's about to be surgically treated anyway. If the retina surgeon feels he can see well enough into your eye to do the surgery, it is possible that the cataract will progress after the pucker surgery such that you will have to have it removed soon. The only reason not to have both problems dealt with now is if your retina doctor thought you would get good vision recovery from the pucker surgery and not need cataract surgery for several more years.
However it works out, your two surgeons MUST talk to each other in advance of any procedure so that everyone is on the same page.
Having a vitrectomy accelerates cataract development. (I believe that it's the lens' exposure to oxygen that the culprit.) If you already have "medium cataracts", you will probably need cataract surgery within a few months of having a vitrectomy.
There's some controversy. By doing both procedures at the same time, you'd avoid the need for a second procedure at a later date. Dr. Steve Charles has written that visual outcomes aren't as good when both procedures are done together, but others disagree.
When both procedures are combined, often it's the retinal surgeon who does both. Frankly, I'd be concerned that the vitrectomy with ERM peeling would take center stage, and the cataract surgery would assume less importance. I'd prefer to have my cataract surgery performed by a surgeon who is experienced at hitting the refractive target.