I suppose it all depends on the trailer tongue and the length of your stinger, but on my '07 Chevy Silverado, with an off the shelf Reese stinger, I have no issues with tailgate interference on the Little Joe
. Unless your current A-frame mounted jack is underneath the open tailgate, there should be no problem with the Ultimate Jack. If you are currently using a side mounted swing jack, just measure from the center of the A-Frame jack mount hole to the edge of your lowered tailgate to see if you will have enough clearance. I can see that on some trailers you may have to rotate or flip up the crank handle to lower the tailgate, but that would only be when you are hitched. I can't see hitching or unhitching with the tailgate down, as the tailgate would interfere with that process.
Using the Jack-E-Up would be redundant with the Ultimate Jack. It's your choice, but with the Ultimate Jack, there is one less item to stow, nor would the Jack-E-Up give me the leveling flexibility I have needed on some very sloped camp sites.
My 2 cents.