Its hit or miss and 100% dependent on the parking lot guard. Some will ask if you are checked in there; some will see the Uber/Lyft ID and wave you through...if it is around park opening I would think they are more strict; tried to go to IG via Lyft through Beach Club once before Early Entry and they let me through but also gave me a warning.
Edited to add this was my experience with Lfyt, not Minnie Van. Never did Minnie Van.
If you want to get really creative and not spend $ you can take the early bus to Hollywood Studios and boat/skyline over (the latter you would need to change at Caribbean Beach).