Only the FP player's dead pile is active so
Uruk Fanatic will only count cards from there. Although piecing together the rules for "active" is like a really cool treasure hunt. If you'll humor me:
Starting point, the entry under "active":
During your turn, only these cards in play are active:
• sites on the adventure path,
• sites in any player's support area,
• your Free Peoples cards,
• your copy of The One Ring, and
• your opponents' Shadow cards.
All other cards in play are inactive. Inactive cards are not affected by the game and do not affect the game...Okay, so how about the cards
not in play? For that we must look elsewhere, like the entry under "dead pile":
Just kidding. It's not there either.
At this point we take a leap of faith (or scour the search results) and check the entry under "spot":
The word spot sets up a requirement for playing a card or using a special ability in conjunction with a noun such as, "To play, spot an Elf." This is equivalent to, "An Elf must be in play and active for you to play this card."
Cards in your dead pile are active during your turn, but they're not in play. You can't spot a card in your dead pile.Voila, and in helper text, no less! Although it still doesn't outright state that the Shadow player's dead pile is inactive, but the implication is there with the "during your turn" bit.
Next challenge: figure out which cards are in play.
The rulebook helpfully neglected that entry completely.