it does have distinctive harmonic limitations.
1. The inabilty to modulate easily to different keys,WHICH IS ONE OF THE GREAT ADVANTAGES OF STANDARD TUNING.
String singer is correct Bensusan is one of the few people who has explored Dadgad extensively.
the reason why Carthy hardly uses dadgad these days, but uses dadeae, or the c based variant of this.. is because it is less limited harmonically than dadgad, And because it allows the player more flexibilty key wise .
Another tuning which has less harmonic limitations than dadgad is orkney tuning, cgcgcd.
dadgad is not the only tuning suited to folk music, or especially irish music, that is just untrue, dadf#ad dgdgbd, dgdgcd, are all tunings that really suit[in the first 2] blues and all suit american 5 string banjo tunes.
irish tunes are very suited to dadeae[ that is why it is known as Irish tuning[check out paul de grae]
finally one of the finest irish gutarists arty mc glynn, uses dadgbe[ drop d], and proves it is eminently suitable for irish music, playing tunes and as well as rhythym.
Dick Gaughan[i believe used a tuning for coppers and brass which was based on the tenor banjo daddae]
Dadgad is ok but it does have certain limitations, in fact more limitations than some other open tunings, check out Martin Carthys opinion on this and martin simpson and nic jones.