We use a split installation that runs fine (touch wood), the main problem we have had in the past was with the data server service crashing when the automatic scheduled caching for the eportal administrator account was carried out at night. The LEA added what I think are the same tweaks that tosca925 mentioned and this along with the fact that I stop (or kill) and restart the data server service after the caching is carried out each night seem to have resolved the issue.
I recently upgraded the eportal server onto a new box and got it up and running following the documentation that comes as part of the install. (Well until I had to go cap in hand to the LEA for the passwords needed to install the certificates for the ssl connection). So wouldn't imagine it can be too onerous to split them up.
I have also played with CMIS/Eportal on VMWare, using VMWare Converter to create a VM of the old Eportal server, which was also the old original CMIS server before they were split. This seems to run fine under VMWare Player, both the CMIS side which I have restored using a backup from the main CMIS server and the Eportal side which will happily connect to the main CMIS server. Apart from some well documented problems with a release of the Converter (which were overcome by downloading a newer version) this in fact went frighteningly well.