You may also be interested in Halberd[1][2] which uses hs-gen-iface[3] to do automatically insert missing imports by finding modules with the desired names. It does not have a vim plugin yet, but I imagine a simplistic one should be easy to make.

Cheers,

Adam

[1] https://github.com/haskell-suite/Halberd

[2] http://hackage.haskell.org/package/halberd

[3] http://hackage.haskell.org/package/hs-gen-iface