Obviously it's the german branch of the IHH, which seems to have been formally registered as a charitable association ("gemeinnütziger Verein") to work within germany. Under german law, anyone can set up a registered association, and if it has a social cause, it will be tax-exempt. There are many thousands of registered associations in germany. Bans are not common, but will be declared if a group is promoting violence; bans have been declared on neo-nazi groups, certain motorcycle clubs, islamist groups, and also certain kurdish organizations.
from the article: Germany outlaws charity over alleged Hamas links