I have SysMon and PHPSysinfo 3.0.16 both working properly on my SME 8 B7
It will work, and PHPSysInfo 3.0.16 does a better job when you can't access the Server Manager Panels.
Also, I tried Cacti for a while, but the learning curve was very steep for the time I had.
In order to get PHPSysInfo 3.0.16 installed while having it protected by admin access, just install phpsysinfo contrib and unzip the 3.0.16 version to /opt/phpsysinfo once the contrib is installed. I believe the proper way is to build a rpm package, but I didn't know how to do that. Or you can just unzip 3.0.16 to an IBay, and protect it that way. Check your error messages in PHPSysInfo for any OpenBaseDir changes you need to make for your IBay install.