HOP! is not strictly speaking part of SkyTeam. So, on a direct routing within Europe that does not involve the Paris hub, you would not get SkyTeam benefits if you are a member of a SkyTeam FFP other than the AF/KL one. This has been explicitly mentioned in the past in HOP! documents for the additional piece of checked baggage. Note that this restriction could change one day.

On the other hand, HOP! operated flights that go to/from the CDG hub are usually treated as standard AF flights. So my personal guess would be that you will enjoy the SkyTeam Elite+ benefits for your DUS-CDG-CFE and return flights. It would be nice if you could tell us what actually happens when you take your flights. Thanks.