Answer
Yes, it is possible to install ArcGIS Server and other ArcGIS products on a single Linux/Solaris machine. To prohibit the two applications from interfering with one another, ArcGIS Server must be installed with a different user account and in a separate location from the other ArcGIS products. The other ArcGIS products must also be installed in Single User mode, not Multiple User mode. Warning messages are displayed, reminding the user of these requirements if conflicts are detected during installation.