Lars,
which users have an issue? could you please be concrete? Because I frankly think you are being a bit vague.
gmp on linux platforms is dynamically linked, so it has absolutely zero implications there. For those wanting to deploy a proprietary appplication on windows or OSX, they merely need to either a) bundle the dylib with the application and suitable install scripting to adjust the load paths. (or build the integer simple version of GHC and navigate choosing dependencies that depend on integer-gmp specifically being installed )
any other problems with industrial usage and libgmp are artifacts of dealing with business or legal staff that have not been educated about how intellectual property law works. Which is business problem rather than a haskell problem.