If you go to www.telefonbuch.de you will find the following:
85 x Dorbert in Germany0 x Thorbert0 x Torbert393 x Thor17 x Thorwald
THORBERT is not listed in Foerstemann’s Altdeutsches Namenbuch (he only has Thorbod; I don’t have the entry DOR, as I didn’t copy all the pages, but there would be a reference under THOR).
ROROLF/DOROLF is mentioned in H.Kaufmanns supplementary volume (1968), but again no DORBERT.
Still I agree to the interpretation “thor” + “beraht.” We probably won’t have to think too hard about the combination of the two, as there often is no semantic connection between name elements.