What kind of "informant" are you using right now? Is it the Dell Open Manage SNMP agent?
If not, may I suggest you start using that? Then you could easily read the temperature using check_SNMP (although you would still have to find out the appropriate OID).
Lists of OIDs for specific hardware are hard to find on the web and apparently everyone's trying to find them out by themselves. I've started making lists of OIDs for various servers on my website. Unfortunately I don't have that many test systems at my disposal right now, but in the future the list will grow rapidly.