I haven't had any problems with the system mib on 9.1.2.
Regarding the serverBytesIn/serverBytesOut and all other counters, the rate must be calculated. FYI, for CPU, the utilization is only available in the mib for TMM utilization, not overal CPU. This also must be calculated from the tmSleep, tmTotal, & TmIdle oids. I believe it is (tmTotal - (TmSleep + TmIdle) / TmTotal)*100, but check ask F5 in the solutions for sure.
I have done some pages in Cacti, and will be publishing a wiki page soon if I can get some projects completed. I modified some templates that a user in the Cacti forum provided, and added a couple for TMM memory and CPU graphing.