If you cannot see any artifacts from the project you have added as a reference in BizTalk, the first thing to check is that you have actually built the project that you are referencing. If you have not first built the referenced project ... then none of the artifacts in that project will be available for inclusion in your main project.
If you are unsure whether you have built the project and you can't be bothered wasting 5 seconds of your life building it again .. then a simple way to check is to click the project name in the reference list of your main project (where you are wanting to include the artifacts). Press F4 to expose the properties window and scroll down the properties list until you come to "Strong Name" if this property has a value of "False" then the project you are referencing has never been built. Rebuild the referenced project and refresh the reference.