For the UV sterilizers, in theory they make sense, but from research I have done, no one has yet been able to fully cure a ich outbreak. In practice, there are so many variables which even the best set up tanks with the most knowledgeable aquarist with the best UV sterilizers, still have not been able to fully cure a ich infestation. Some always manages to survive (not pass through UV) and keep the water contaminated (even with daily water changes/vacuuming). There have even been reports that some ich may go through all it's lifestages within the host (not common, but I guess it's rare possible occurrence).
Now UV's are a great tool that do benefit fish health, increase redox potential and kill free floating pathogens. Even if someone did manage to actually fully cure a ich outbreak with UV sterilizers as the only treatment, then great, but given not many/any are able to succeed, chances of most users trying to eradicate ich with just a UV are very slim.
And not all UV's are made the same (different classes, UV clarifier vs sterilizer). The ones that would actually work in killing free floating ich, do cost quite a bit. Significantly more than any other treatment for ich. But yes, UV's are useful in their own right, I just wouldn't recommend it as an efficient ich cure. If you are considering getting a UV for other purposes, then go ahead and try it if you got it.
But anyways, for the Corys at 82*F, they can tolerate that fairly well (summer temps), but much higher and they can really start to stress. Which stress is not a wanted addition as the fish are already stressed and weakened by the ich infestation. Plants should be fine at 82*F as well.
With Kordon Ich Attack (and other meds), raising the temp is not at all necessary. You do want to find a balance though, on one hand you want to speed the ich lifecycle up to end treatment quicker since long durations of exposure to meds is also harmful/stressful, and on the other hand, you want to reduce exposure time to meds, but you also don't want to induce excess stress from the uncomfortable temps. So you find a balance between stress more so through heat, or stress through med exposure.
With Ich Attack, I would not worry at all since the fish tolerate it extremely well. There is still the stress from heat. When using Ich Attack, you could either use no heat increase at all, or just elevate temps to 82-84*F max (again it's not necessary, but it can end treatment time sooner and save your a bit on med dosing since you wouldn't have to dose as many days. I would personally just say 79-82*F, as higher stress solely from the heat is doing more harm than good).
Make sure to remove activated carbon, turn off UV's, and maybe even skimmers, when using meds for treatment. Be sure to treat for an additional 3-4 days after no more visible ich spots/cysts are seen. Increasing surface agitation may be recommended. If the ich outbreak has progressed to a severe case, doubling the dosage may be advised (even says so on bottle).