If you never ever want to uninstall or upgrade any of your current mods, you may delete all such directories.
Otherwise the answer is "no". Sorry! Those directories contain the raw data files from which a mod is installed (this is needed when you upgrade a mod you installed before this one) and old "backup" copies of your game files from before you installed the mod (this is needed when you uninstall).
WinNT/XP/2K? You can right click on that folder and say "compress this folder" to save a bit of space if you want to. You can also put them all away somewhere, as long as you restore them all before doing any mod upgrades/uninstalls.