Any type of exercise is bound to improve a persons blood pressure. The one you have asked about, resistance/strength training falls under anaerobic exercise, where muscles are trained and developed for more power over shorter time periods. This will cause an increase in muscle mass, which will require the heart to work more, which might potentially lead to an increase in blood pressure. But again, if resistance training is combined with the other type of exercise, which is aerobic exercise, the positive effects it can have on the body are very good in terms of blood pressure. Speaking as one who needs to exercise more, be it resistance training or aerobic exercise, I can vouch for the lowering effect exercise in general has on blood pressure. We were meant to move, not sit still; too much in one way or the other will have a toll on the body in a negative fashion.