There are several cases where it is necessary to put thirdparty (non jboss) artifacts in the Maven repository. All thirdparty jars should fall into one of the following categories: the jar is available in an existing Maven repository, the unmodified binaries (jars) are not available and need to be uploaded, or the thirdparty project needs to be rebuilt from source possibly including patches.
Check Existing Repositories
The first thing to check is whether the artifact is available in an existing repository. In this case the artifact (jar) may already be available via the "public" repository group which contains several thirdparty repository. If the artifact is available in a thirdparty repository which is not included in the "public" group, submit a jira issue (https://jira.jboss.org/browse/JBBUILD) and request that the repository be added.
Upload an Unmodified Thirdparty Jar
If the jar you need is not available in any existing Maven repository, and is only available via a downloadable distribution such as a zip file, then you should upload the jar to the "JBoss Thirdparty Uploads" repository. For more information related to this, see Uploading a Thirdparty Artifact.
Deploy a Rebuilt Thirdparty Project
Thirdparty projects that are built from source before uploading should be deployed using the same steps you would use to deploy a JBoss project. At a minimum the POM will need to be patched (or created from scratch for a non-Maven project). The deployment URL for a rebuilt thirdparty project is exactly the same as for a JBoss project. For more information about this see Maven Deploying a Release.