Shouldn't the OS partition also be listed as active?
Nope, it should be when you are done with the whole thing. However I think you can only have 1 Active partition per physical hdd or your system won't know which to boot from.
Can I safely delete the Recovery partition?
NO! As that partition is the Active one and the 'System' bit tells us where your computer is booting from, remove it and your PC won't boot properly. The 'Boot' bit on the OS partition tells you where the OS resides not where it actually boots from, just a funny little windows-ism.
The safest way to do it is to move the boot files over to the OS partition (repair if required) and set the OS partition to active, but before all that make sure you have bootable CD/USB so if anything screws up you can restore your system to a workable state or reset the partition settings.
This may help: http://windowssecrets.com/forums/showthread.php/138153-A-3-Hour-Tour
. Although I know your problem is creating a drive image with the Dell recovery partition, so the full backup image bit may not be possible.
I think mkk highlighted in the other thread about using Acronis which I have found more reliable then windows backup over the years. Good luck and remember before you try anything... backup, backup and backup!