DC locomotives can be run on some DCC systems, but you'd have to look at them all and their specs to find out. I have the Digitrax Super Empire Builder using the DB150 base unit and twin DT400 throttles. Digitrax's literature says you can run DC locomotives using Add "00" on the throttle. I tried it before I installed a decoder in a beautiful Proto 2000 0-6-0. The drive mechanism whined, growled, and squealed due to the frequency and zero stretching, but when I dialed up enough voltage (speed steps) it began to move. I only did this for about five seconds...for giggles...but I wasn't giggling. I would never try it again. In any event, people who ran them for longer periods soon decided it wasn't worth it, and those who forgot and left DC locos on DCC rails without making them move fried their motors due to overheating. Some lost their shells to the heat as well.
The others have addressed DCC-equipped locomotives used on DC powered rails. Almost every decoder made after about 2005 is 'dual mode', which conforms to the NMRA standards and allows the decoder to sense which it is on the rails, and thence to behave accordingly. Some decoders had the bad habit of jack rabbit starts and running away as soon as the DCC was powered up. The cure was to eliminate the ability to sense DC, and that was by setting the appropriate value in CV29. For most of us, that would be a value of 34.