It might wear the battery out quicker. You might get a few months less out of it continually discharging it like that. So yes, it will stress the battery, but no, it's not beyond the safe level for that battery. It's probably better to charge it at a higher overall voltage. Instead of running it down to 3.2v, stop at maybe 3.5 or 3.6 when possible.
The tank is always gonna get hot running a coil like that in it. As long as it's ambient heat going to the battery and not heat coming from the battery itself, I wouldn't be extremely concerned about it. Most, though not all of these batteries can withstand significantly warm operating temperatures when running well within their amp limits. A little temperature gain is a given due to the high current. Just bear in mind that the amount of external heat they can withstand decreases as the amount of current draw increases.
I think the general rule of thumb is to not let them get much hotter than 10 degrees over room temperature, though I believe the Samsung 25r's specify a max discharge temperature of something like 75C, which would be well over 100F. Wouldn't take that as gospel, but it's something to consider. I wouldn't let them get nearly that hot while sub-ohming. However "warm to the touch" seems acceptable.
A battery that's only a little below body temperature will feel pretty warm to the touch (perhaps even a little hot to some,) but it's generally nothing to worry about with these batteries. If a battery ever gets like, seriously-uncomfortably hot to the touch, I would take it out, let it cool to room temp, ensure that the resting voltage is 3v or higher, charge it, check the voltage and let it sit for a day. If the voltage is the same the next day, then you're most likely good to go. I would take care not to make a habit out of that, though.
It's more of a concern if they're warm while charging. They can take a surprising amount of heat when they're dishing out current, but not at all when they're taking it in.
Of course, it's always better to avoid any heat traveling to your batteries. The main risk is that you may not be able to tell what is acceptable heat and what is a sign that your battery is actually failing. Use common sense and you'll both be fine.
