Most likely -- yes. Let us go with the US F-16 deal for now. Ordnance from the MIGs are probably not compatible with the F-16, so there is no logic in keeping them. Send'em all to Ukraine.
Am Air Force, so am always going to be partial to air force people, no matter their country.
Pilots are normally valuable assets. As long as there is a functional airfield, jets will fly. But in this particular situation with the Ukrainians, the longer the absence of the VKS over Ukrainian airspace, the greater the value of the Ukrainian pilots. This valuation is tactical. As long as the VKS either failed or refused to achieve air superiority over Ukraine, maybe they refused for some mysterious tactics we do not know yet, Ukrainian pilots must act quickly to deny airspace to the VKS and to attack Russian ground forces, especially that stalled supply convoy. The longer and greater presence of Ukrainian jets over Ukrainian ground forces, the morale factor cannot be understated. So whatever amount of pilots Ukraine have, those guys are national treasure right now.
That said, it will not be easy taking over the Polish MIGs.
For starter, how will the Ukrainian pilots get over to Germany? How many jets determine how many pilots.
Next, the Ukrainian pilots will have to examine the Polish MIGs to see what are the differences, and there
WILL be at least minor differences between what they are used to vs what the Poles have done to these MIGs. But am willing to say that the Ukrainians pilots will be able to adjust.
Next, the Ukrainian pilots will have to make familiarization or functional check flights. They have to know how each jet perform in the air. All jets are essentially hand built, no matter the country. So inevitably, there will be the usual 'product variations' but this will not be a major problem. As long as the pilots are comfortable with the functional check flights, they will accept the jets. But they have to make these flights.
Next, on the return trip to Ukraine, will these jets be armed? No doubt the Russians will know of this deal so now, even though the VKS is largely absent over Ukrainian airspace, I am
%100 confident that the VKS will sortie to hunt them down. From my personal perspective, it would be foolish not to preempt the Ukrainians, and the Ukrainians would be foolish not to assume the same, so most likely, the return flights will be armed and treated as a combat sortie. The Americans, the Germans, and the Poles would follow the same reasoning, so the MIGs will be armed with air-air missiles to defend themselves until they make it home and begin to use the jets for other missions.
For the long term, if these MIGs make it to Ukrainian hands, and if the VKS do not show whatever mysterious tactics they have been withholding or that the VKS is truly incompetent in this war, the fight will be tougher for Russia.