Here's one caveat: haskell-names cannot use ghc's interface files to get information about installed modules. Instead, it maintains its own interface files. Which means that you'll have to install separately all packages that you need to access using the hs-gen-iface compiler, as described in the README. Additionally, not all packages that can be compiled by ghc can be compiled by haskell-names yet. It's up to you and other ghc-mod users to decide whether this is acceptable.
-- Carlo Hamalainen http://carlo-hamalainen.net