It does specifically say they are subject to Dispel Magic, so that would work. However, since every epic spell is researched individually, you shouldn't be able to use the standard "I cast the same spell to counter it" counterspelling action. (Even if you choose one from the book, just add an extra silent Q in the middle of the name and BAM, uncounterable).
I would allow countering Epic Spells. Unlike Souljourner, I'd even allow countering of spells with the exact same effects (such as ones pulled from the book). If you start letting people put silent qs in their spell names, what's to stop them from trying the same thing by researching Mass Haqste, Fireqball, or Haqrm?
I think I found my answer. The ELH presents a sample spell called "Epic Counterspelling" which seems to allow for the countering of epic spells. Thanks for the answers, folks!