Hi Basil,
Do one of the following things:
1) If you use create datum when creating the feature you can then modify the angle within the feature itself.
2) Or, you can modify the angle by going to the model tree and clicking the plus sign and then selecting the datum, then RMB and edit. {This is for WildFire 2 for 2001 you need to select feature and then modify}
3) If you create an angled datum plane and then select this for your left or right sketcher orientation and then you can sketch an ellipse at any angle you need.
I hope this is helpful.