I had a similar issue this year with my new company and the broker becoming less engaged and essentially not providing the support we needed. However, I have not heard of one broker representing one carrier and another, another carrier. From my understanding, a broker can carry just about any carrier out there. It would raise a red flag in my mind if they push a particular carrier that may not provide the best coverage for your employees. Seems to be a biased offering that I would not want to be a part of. I would simply initiate with a reputable broker and have them shop you to all carriers. Competition is good but I would not suggest segregating the carriers to different brokerage firms.