Orks are a random force of nature in WH40K.
They just are and their purpose and desires are very basic. Reproduce, spread. They take no sides, not even their own, which should give you a great indication in exactly how random in nature they are.
SO in terms of galactic politics they play absolutely zero politics. They play a part only in so much as they must be prepared for, if possible, like any civilisation must prepare for any great natural disaster (particularly if you live in or around known Ork infestated space). So for example, you built your cities in an earthquake prone area, then you'd prepare and build for earthquake resistance. You can't proof against it but you can try to minimise its effects.