I disagree. At the end of ROTK, Frodo meets Wormtongue again, and shows pity on him -- even extending kindness. Wormtongue is touched by this and wants to accept Frodo's offer, but decides not to and makes a fateful decision. (I'd reveal more but don't want to spoil anything for the un-read).
Wormtongue is a despicable character, but as is typical with Tolkien, not utterly without humanity. I saw that tear as a tear of regret and guilt for what he has done. He wanted to rule, he wanted Eowyn, and in his shock at seeing Saruman's army, realizes that his dreams of power and "happiness" are gone forever. Even if the dark forces win, he'll never be more than a puppet. Saroman, he realizes, has the real power, and will never share it.
And, just a little nit-pick. How the hell could Wormtongue have been surprised by the army Saruman compiled. For crying out loud, there's 20,000 screaming orcs outside the window and he didn't notice?