Yes.....you are right, if he already have installed SQL 2008, then there is no need for new liscense for SSIS. SSIS comes with SQL.

I think the main concern for him that his developer is not able to build/design ssis packages through his local machine.

If I were you than I would reinstall the SQL CLient tools and SSIS service agian in developer local machine. I am thinking that something went wrong during the installing process.

You still have to have SSIS service running locally (in developer local box) to build and design ssis packages. Installing just BIDS is, i think, not enough. Correct me here someone if a I am wrong.