Waterproof connectors are suited for being buried directly in the dirt (hence the direct burial), and will work fine in your situtation. You hate to have to add more splices than you need to sprinkler system wiring, but if it is unavoidable, and you do not want to run all new wires, you really have no other option. Could this cause more problem later down the road? It is a possibility, but if you take your time and make the connections right, you shouldn't have a problem.
Tony Posey
Ridge Run Landscapes