I had decoders installed in two of my locomotives; a Kato SD38-2 and an Athearn SD45 locomotive. Both locomotives were DC and again had decoders placed in them; from what I understand you don't want to leave a DC loco on a DCC track, but can you leave a DCC loco that was previously DC on a DC track and will it still operate as though the decoder was never put in it on that DC system?
As long as DC mode has not been disabled in the decoder they are most likely fine. Most modern decoders are dual mode. You might want to confirm with your installer that these are indeed dual mode. Some decoders like early Soundtraxx would smoke on a DC layout.
Simon Modelling CB&Q and Wabash See my slowly evolving layout on my picturetrail site http://www.picturetrail.com/simontrains and our videos at http://www.youtube.com/user/MrCrispybake?feature=mhum