Is RawTherapee an interface for dcraw?

No. RawTherapee uses dcraw only for decoding of the raw files. It is not commonly known, but dcraw is the basis of the decoding engines of almost all raw converter software (including Photoshop, LightZone, RawShooter, etc.).

All the algorithms of the image processing steps (including the demosaicing) are RawTherapee's own methods.