DITMAR is indeed a variant of
DIETMAR.
ROGWOLD seems to be a variant of RAGWALT ("counsil" + "rule")
ROGNEDA I don't know. Probably
Satu can tell us, if there is a relation to RAGNHEIÐUR (From the Old Norse name Ragnheiðr, which meant "bright advice" from the elements regin "advice, counsel" and heiðr "brightness". btn)