USCG has historically always had ties to the DoD, has been working with DEA for years, and now the DHS also has it's hooks into them. Several USCG ships operate (or were when I was over there) off Iraq and Kuwait in support of OIF in patrolling those waters and inspecting ships in that region.
USCG still have ties also to the DOT in regards to waterways, and, IIRC, to NOAA and Corps of Engineers, unless that has changed with DHS involvement these past few years.
Their mission statement just includes such a broad range of activities that overlap into so many other agencies spheres of influence. Im' not saying they answer to those agencies, but they work with them on a big scale.
If they fall solely under the DHS these days, well, I can't believe that bodes well for what has always been an exemplary service in the past. If anything can screw up the USCG, it's the DHS.