Yes, you can put several items in one rrd file. Here is a snip from my nagiostat.conf file that shows the graph was created to store "rta" round trip average for a ping, plus "pktloss" packet loss.
RRDCreateTemplate ping_5min --step 300 DS:rta:GAUGE:600:0:5000 DS:Pktloss:GAUGE:600:0:100 RRA:AVERAGE:0.5:1:396 RRA:AVERAGE:0.5:6:336 RRA:AVERAGE:0.5:24:480 RRA:AVERAGE:0.5:234:480
When the nagios check_fping command is ran, it gives the values for both rta and pktloss. The output of the command is sent to nagiostat, it then parses the output, and stuffs the data in the rrd. So if your check_command that looks at the partitions can give you results for all 6 partitions, then create the line in the nagiostat.conf that will accomplish the create/parsing.