What version of ghc?  Were there any linking errors
when the hat package was built?

GHC 6.4.2 and no linking errors that I know of. GHC gave a few compilation warnings, but that is all.
The output from ghc-pkg describe hat shows the following:

exposed: True
exposed-modules: [list of hat modules...]
hidden-modules:
import-dirs: /usr/lib/ghc-6.4.2/imports/hat
library-dirs: /usr/lib/ghc- 6.4.2

No other directory settings are set. Is this correct?