Watch the Arpeggiated Chords online guitar lesson by Jennifer Batten from Rock Sauce for Rhythm Guitar
The technique of combining open strings with fretted notes is very common in country style guitar playing. It adds another level of lushness to an arpeggiated chord. I've also used string slides and hammer ons while arpeggiating, to add more notes. Another technique here is to play a D major triad chord made of harmonics.