I can't seem to find any load data specific Winchester 115gr STHP bullets.  For all intents and purposes, can I treat these like jacketed hollow points and use JHP load data?

thats what I would do. Make sure you start with the min charge and work your way up just in case.

Yes, but understand that all guns are different and I have found some book loads that are excessive in my S&W.

When you are working-up your load, measure case expansion with your caliper. In my guns, factory standard pressure ammo expands to .391" while +P+ expands to .394". 9mm chambers are conical and have case walls that taper toward the case mouth. The higher the pressure, the more the case expands. Use that together with published data.

Good info.  The more reloading I do, the more I realize that published load data is at best a guideline.  They can measure pressures and velocity for their test firearm, but at the end of the day, every load will behave differently in different firearms.

I'll watch for pressure problems.  Probably load up just 10 rounds to start with and see how they behave.

Midway's 9MM LoadMap manual lists the 115 Win ST/HP bullet. Since seating depth changes pressures especially in the 9MM these loads from Midways LoadMap are just for comparison only. I picked a couple powders and the same charge with different manufacturers 115 grain bullets.
Win 115gr ST/HP  AA#5–– 6.3 grains––29600psi––1097fps
                            Unique––5.0––––––––-24100––––––1084
__________________________
Win 115 JHP          AA#5 ––6.3––––––––28100––––––-1108
                             Unique––5.0––––––––26900––––––-1076
_________________________
Win 115 fmj     AA#5 ––6.3––––-28100––––1098
                       Unique––5.0––25300––1060
_________________
Speer 115 JHP     AA#5––6.3––31400––1127
                          Unique––5.0––28400––1090
___________________
Speer 115 Gold Dot     AA#5––6.3––-28300––1084
                                  Unique––5.0––26400––––1055
___________________
Sierra 115 JHP   AA#5––no load listed for the above charge level- 5.7 grains gave 31200 psi and 1079 fps
                          Unique––5.0 is max or near it for the Sierra 115 JHP tested––-32400psi––1139 fps
_______________________
Remington 115 JHP   AA#5––6.3––31700––1124
                                Unique––5.0––28500––1088
_____________________
Nosler 115 JHP       AA#5 load listed for the above charge level is too high––-5.7 grains gave 30000 psi and 1070 fps
____________________
Hornady 115 HP/XTP   AA#5 ––  6.3 grains which is max or above––33700 psi––1156 fps
                                   Unique––5.0 ––31100––1120
 These loads are for comparison ONLY. It does show there are differences in bullets and data for them. Seating overall length would change these numbers for psi and it's Midways testing using their components and equipment. Some of the bullets showed in their tests that 6.3 grains of AA#5 and 5.0 grains of Unique to be over max or near max.
  What powder and primer you using?

Using Hodgdon HS-6 and, unfortunately because it's all I can find, Federal small pistol magnum primers.  I plan to start a bit below starting load owing the magnum primers.  The firearm I'm loading for is a Hi Point 9mm carbine.  16 inch barrel, blowback operated.

Just for some more info using HS-6 and the Win 115 ST/HP from Midway Usa's 9MM LoadMap.
They seated the ST/HP at 1.130" overall length, used Remington cases and Win SP primers. Testing in a universal receiver 4" barrel.
HS-6 powder
START 6.1 grains––27100 psi––1084 fps
6.2––28100-1101
6.3-29100-1118
6.4-30100-1135
6.5-31100-1152
They say to use caution when loading from 6.5-6.7 grains with 6.7 being maximum in their test. I'd stop at 6.5 and consider it max.I've found the LoadMap data to be pretty close using 9mm and 45 acp data from the LoadMap series of manuals. Do start low and work up and use this info to cross-reference other data using HS-6.  I've got a Kel-Tec sub-2000 carbine and shoot 124 grain bullets in it.

Frankly, I'll probably start at 5.9 grains, owing to the magnum vs standard primers.

BTW, where can you get one of those Midway loadmaps?