Here's a tip: don't be a d!ck on the flight deck. I've been instructing for a long time at the FTU and rarely ever yelled at students...and the times I did, I was yelling for them to let go of the flight controls because they were trying to kill me. I've seen lots of great instructors who take the time to explain to their studs what's going on and why they are doing what they are doing. And I've seen some real a$$holes who think it's cool to yell at the kids and make them auger in (grade-wise) on a ride...I don't get it. You're an INSTRUCTOR pilot. Even as an evaluator, I just sit there, be a good copilot, and if they are starting to go off the ranch I'll ask the dreaded "so, what should we be doing now" phrase. But I don't yell at people unless there's a very good reason to.
Oh, and FWIW, dudes who don't yell at their studs later in life weren't necessarily "weak in UPT". Nice argument, though (sarcasm alert).
Break, break...
And for the OP...I generally agree that UPT will teach you what you need to know. Plenty of zero-timers have walked through the doors and graduated with their wings just fine. That being said, I arrived at UPT having already been a rated pilot (Army helo pilot), and I knew how to fly on instruments. It was still a lot of work (lots of local area procedures, etc), but while I was focusing on the details, my fellow classmates were still trying to figure out how to fly basic instrument procedures (ie, climbing turns on instruments, etc). I already had that stuff down pat, and I cruised through the instrument portion.
Each person's mileage may vary -there were regional airline FOs at UPT that struggled with every aspect of the program- but IF you have the money, it probably wouldn't hurt to practice doing some basic instrument flying. I don't mean flying an ILS or a STAR, but I mean learning how to fly straight and level, doing climbs, descents, turns and eventually climbing turns on instruments. Having some of that experience in your back pocket might not seal the DG (Distinguished Graduate) award for you, but it might make life just slightly easier for you and increase your confidence flying IFR. I'll add that if you do decide to get some IMC flying experience, find a CFI that's been an ex-airline guy or ex-military...they tend to be more regimented which is what you need to prepare you for military flying.