In order to use an asset inside a host application (UE4, Unity, Maya C4D), Houdini must be installed on the same computer as the host and a license that can run Houdini Engine must be accessible.
If you are running Houdini (CORE or FX) on your computer then the Engine will use that same Houdini (CORE or FX) license and you are good to go. If someone else needs to use the asset but doesn't have a Houdini license then they will need a Houdini Engine license. This license is only needed when you first create the asset and any time you recook it by modifying a parameter or other input value.
When you save your level/scene and open it again a cached version of the results are in place and a recook isn't needed so a license isn't pulled until you make a change.
Therefore a pool of floating engine licenses will often serve a larger team rather than one per artist. Unless of course the assets are being updated regularly at which time more licenses will be required.