Just confirming my new understanding:
When creating a minipool (arb with rETH mint)
assignDeposits() gets called, which is the function that will actually “create space” in the deposit pool by assigning it to a particular minipool.
I think I had conflated the “creating space” idea with the part where RP actually deposits its share, but for arb we only care about when the space is created. Looks like it should work 
.
When exiting (arb with rETH burn)
I’m a little less clear here.
My first read (I’m a solidity and RP contract newb) looks like distributeBalance has a different effect when staking (status==MiniPoolStatus.Staking) vs when the validator has exited (status==MiniPoolStatus.Withdrawable). It looks like the 14-day check is in place if status==MiniPoolStatus.Withdrawable?
If I’m understanding those statuses right, I think flashbots would work for this arb need.
Update: knoshua explained and showed me that this wouldn’t work, because the oDAO sets the state to Withdrawable. So it’ll be an open race with everyone 