It is possible to monitor fan speeds and temperatures on Dell Poweredge servers under Linux. You can achieve this by reading out the IPMI data that is available on the system.
I used the steps on this website to buffer the data gathered by IPMI to use in Cacti.
However, in addition to Cacti I also use Munin to monitor various system parameters. Wouldn’t it be nice to incorporate graphs for fan speeds and temperatures in Munin? I thought so, so I developed a way to do this.