Lufthansa upgrades to paid fare classes (e.g. Z, D, C). Aegean does not, they upgrade only to a non-earning class normally used for free award flights (I-class). This means that with Aegean there is much less availability for upgrades, but on the flipside with LH the upgrade price is dynamic and may be (very) high depending on the fare class you will be upgraded into.
When flying non-earning classes it is typically possible to request earning based on the previous (earning) economy fare. The crediting may not be automatic though. You may have to talk to UA to get it credited properly (as P).