The idea of using "mindfulness" training in treating borderline personality disorder may seem strange at first. However, most borderlines would benefit substantially from developing the ability to take a step back from their intense reactions and think more clearly about handling their emotions. Mindfulness training seems like a plausible way of doing this.
However, there is a potential problem with "selective borrowing" from a treatment approach which works well as a complete package. A componet taken in isolation may not work in the same way as it does in combination with the rest of the treatment.
In Marsha Linehan's approach, she emphasizes the importance of the therapist's validating the client's emotions at the same time as he or she works to help the client deal with them more adaptively. If mindfulness training is used in isolation, the client could easily experience the therapist as invalidating his or her feelings. If this occurs, I would expect the client to have an intense negative reaction within the session and to become more symptomatic following the sessions. It takes some delicacy to simultaneously validate feelings and help the client handle them differently.