And to answer your main question, the Romans did adopt the Greek pantheon into their own religious system, but the Romans often times added their own "flavor" to the deities, making them not 100% identical with their Geek counterparts.
Also, there's so much information on the Greek and Roman deities that merging the pages together would make the merged page too long and unwieldy.
I noticed you put Neptune as Poseidon's alias. I removed it because there is already a "Roman Equivalent" section on the infobox.
- KRJones87