I've always had a slouching problem since i was little, but after about a year of pole dancing people started to tell me how much my posture has improved! I believe that part of the reason is that my back has gotten stronger. The other part of the reason i think is flexibility improvement of the chest and shoulders.
I always do specific exercises right before i pole, and i can feel like they help me keep my back straighter while i pole dance.. then i do them again when i am done working out/ dancing.
Here are the exercises:
1) Standing to the left of your pole, grasp the pole with your right hand, arm straight. Height should be a little higher than shoulders. Then turn/twist your body towards the left, and you should feel a good stretch in your shoulder. If you lower your arm to shoulder height, then you'll get more of a chest stretch. Do both.
2) Same as 1st exercise, but turn your hand so that thumb is down.. this stretches another part of your shoulder, but not your chest. Still good to do though.
3) After you've done exercises 1&2 with both arms (obviously left arm will be with you to right side of pole, & turning body right), stand with your back to the pole, feet touching the base, clasp your hands together behind the pole, & lean forward, leading with your chest. Be very gentle when you pull yourself back into the pole to release the stretch.
4) This one is a yoga pose, but i don't know what it's called. You kneel on the floor, knees apart, but don't sit on your legs; keep your body from the knees & up straight. Don't have your toes curled under; keep them flat. Engaging your abs, slowly lean back (as if doing a back bend kind of), while reaching back with your hands and grabbing your heels. This is a great one for counter-acting the upper back hunch.
I don't know if you do these already, but hope it helps you some.. they've definitely helped me a lot!
Disclaimer: I'm not a fitness expert, so if anyone else has an opinion on these exercises, or can add something i might be missing in technique/safety, please do let me/us know!