Correct me if I'm wrong, I would summarize your requirements as follows:
- you need some "A-box" reasoning, but you are fine with a rule-based approach
- the object-oriented integration Drools provides is quite convenient
- you have large data sets for which an opportunistic, "query-oriented" approach
would work better rather than a fully generative "forward chaining" approach

Drools "hybrid-chaining" approach could be very useful here - I'm not sure how
well documented it is, and how you are planning to use it, but it would be interesting
to see one of your rules - even "stripped" of the details you don't want to show -
to discuss the behaviour of the engine and its implications.

I had a use case apparently very similar to yours some time ago.. I'm working even
now on some experimental forms of rule/object/ontology integration. The "trait"
feature might be an alternative to the explicit addition of classes to objects .. it was
enhanced a few days ago to support updates and modifications.
If you have an ontology to begin with, you might also be interested in the ontology -> class
conversion tool I'm working on even now

Davide