Vector data stored in a database is covered by OGC's Simple Features and WKT. Databases indeed implement these standards. Some databases such as Oracle, PostGIS extend their support to rasters.
Is there an equivalent to WKT and Simple Features for rasters?
No there is not. PostGIS raster does try to follow similar to OGC SF standard as much as possible by providing similar functions for raster as we have for geometry. E.g. ST_Intersects, ST_Covers, ST_Intersection.
That's more so to make it easier for users to work with raster if they know how to work with geometry already.
