Hi Dawn,
I?m not really sure about the 'borders' (boundaries ?) of Ostfriesland - but
it lies in today Niedersachsen (Lower Saxony)
So I don`t know wether the following link is helpfull:
http://www.hollwege.com/index2.html
you might know already this:
http://www.museumstuff.com/zg.cgi?ln=Oltmanns&fn=melissa
and this:
and this:
http://boards.ancestry.com/surnames.oltmanns/mb.ashx
Greetings from Bavaria
Christine