Can the 9th bhava in the natal chart relate to marriage?
Since the Navamsa chart correlates to the 9th bhava in the natal chart, and the navamsa relates to the topic of marriage (if that's correct?), does that mean in the natal chart the 9th bhava can be looked at when researching marriage/spouse (rather than just the 7th bhava/darakaraka/etc)?
Yes, 7th house is relationship with others in general, 9th house is like the path we commit to, including marriage.
Wow! I absolutely love that concept, can't believe I hadn't realised it before hahaha