RRDtool is required to get the nagiosgraph Addon working correctly. 

"RRDtool is the OpenSource industry standard, high performance data logging and graphing system for time series data.  Use it to write your custom monitoring shell scripts or create whole applications using its Perl, Python, Ruby, TCL or PHP bindings." - http://oss.oetiker.ch/rrdtool/

I follwed the instructions outlined in the package.  I did run into one issue since I had to install libart-2.0 from source as well.  Read about the missing libart error/fix here.  Also to avoid an "undefined symbol: art_alloc" issue, I had to install a specific version of libart and you can find out about that undefined art_alloc issue here.