I agree with your response to your own question :-)  When we first implemented ControlCenter in our environment we used local disk for the very same reasons you were initially unsure about using SAN capacity. Over time there were several discussions around this decision, and at least one point were we upgraded CC and could no longer provide the "required" space for the database drive because of the limits of the internal drives.  We had the opportunity to completely rebuild the CC infrastructure two years ago (including rearchitecting and building on new hardware). This time around we opted to provision the servers from our DMX3 instead of local disk. The reasons were mostly the same as the ones you came up with. There was one additional thing that we considered as well though. While CC is good for monitoring and alerting on our Symmetrix environment we have found that actually allocation work goes better through a combination of CLI and SMC (although we still do most of the masking through CC). Because of this, CC is no longer a critical component for addressing an incident that might affect the server's connectivity (and thus CC's functionality). I do use it to aid in troubleshooting when it is available, but if it isn't it doesn't prevent us troubleshooting and resolving the incident.
We are thinking about replacing our ECC Infrastructure Server.  Our current ECC Infrastructure (1 x host Infrastructure) only has 2 x 73 GB drives inside for OS.  They put the ECC Database, Backups, etc, on SAN Drives.  I always thought that the ECC Server should have internal storage for ECC software, database, etc.  If the SAN goes down for any reason, then your ECC Server goes down and you can't use ECC to fix the problem!  Is there a best practice that says "You should put your ECC software and database on internal drives on the ECC Server."?       Stuart
ECC Config Best Practice: Should I use SAN Drives to hold my ECC Database?