My understanding is that some key personnel is of Hamburg Airways / Hamburg International origin, so there is staff around that knows how to run an airline. If successfully is another question... Sundair's founder hails from Stralsund and he has gone on the record that it does not matter where an airline's administration is headquartered. The idea behind the location could well be that labor and facilities are rather inexpensive in that region.
Sundair is 50 per cent owned by Schauinsland Reisen, a German tour operator that will celebrate its 100year anniversary in 2018. It has a turnover of roughly 1bn EUR. Sundair is Schauinsland's in-house airline.