Thanks for clarifying, though I do agree with hornet that it is a bit of a loaded question.
First off, as I have written and as hornet says, most that are eliminated from IFS cannot land the plane. If you invest time and money into a PPL, you will be able to land an aircraft, and as a result could go to IFS with almost no shot of being eliminated. As a result of your extra flying time, you will also have a solid start on UPT, though you must be very ready to re-learn the Air Force way of flying.
However, for those that go to IFS with little to no flight time, IFS can definitely be a challenge because in all but one of your ten pre-solo flights, you may only get three patterns per flight to practice landing. That's really not tons of landing exposure, and IFS is not designed to allow much extra practice or additional sorties. The premise is to see if the student can learn at the pace supposedly required in UPT. If you can't, you'll be eliminated.
UPT is similar in the sense that the learning curve must be picked up within the first ten or eleven rides in order to solo. However, there is a little more flexibility built into the T-6 syllabus, and you have a little more control of your own training. I'd also argue that there is much more investment in the student at UPT in the sense that they do not want to wash out students. As a result, more effort will be put into helping them succeed instead of the IFS mentality of seeing if they can learn at the prescribed pace and cutting them if not. So to sort of answer the question, I'd argue it would be possible for someone that did not complete IFS to complete the UPT, but that student would more likely than not struggle through the program.
Just for my own background, I didn't have the best luck with weather while doing USAFA airmanship, and as a result only got 5 rides during soaring, and another 5 rides during powered flight. In those 5 rides, I never really put the T-53 on the ground, but even that exposure was enough that I was able to learn on the DA-20 fairly quickly. However, I'd disagree with hornetguy and argue that the T-6 is much more challenging than the DA-20 to land. But that was just my experience.
It's a prerequisite for UPT if you don't have a PPL. I was wondering if skipping IFS, with the inherent risk of busting IFS, actually might benefit anyone interested in getting winged. In your opinion....can you imagine someone that was unable to pass IFS being able to pass UPT?
Oh, that's a loaded question! My opinion, and only that, is YES. The two major factors, so I hear, on DQs from IFS are the hazing factor and landing. Hazing factor in UPT can be limited if they find it's causing issues, but they are less lenient in IFS. However landing is a bigger issue. A DA-20 is like a glider and landing, for first timers in a plane, is tough. A T-6 has very different performance and I don't think landings are as tough in terms of strange factors. I have a friend who did powered flight and was not allowed to solo because she couldn't get landings. She went on to IFS and passed (prior XP helped) and was successful in ENJJPT.