No, it's not about exposure therapy. It's actually much closer to buddhist teachings-- of mindfulness. To feel the emotion and how it is in your body and let it go, instead of then thinking "I'm mad. It's so and so's fault. They don't really love me." etc. etc.... which continues the feeling, makes it worse and then turns it into something that isn't even based on reality.
There's a workbook you can get online the DBT workbook (I got one through Amazon). I highly recommend getting one and just taking a good look so you can see what it's about.
It's not about just exposing yourself and "dealing". It gives you actual tools to deal with emotions better.
A good therapist will really make a big difference though. I'd look for a therapist who specializes in DBT specifically, then question them and find one that is at least open to poly, if not experienced with it.
My counselor does DBT and specializes in GLBT, BDSM and poly clients. They are out there, you just have to do a little research and ask them.
Also... there's nothing wrong with (and a lot of good can come from), being up front with your counselor and telling them you suspect you MAY have borderline personality disorder. They will be better at figuring out if you do, or if you just have some other issues, etc. (Interestingly, ADHD shares a lot of the same symptoms as BPD, with a few differences, though.)
It's no different than going to the doctor and telling them what's hurting so they can check into it and help you fix it.