I endorse this flavor. It does less to persist various myths about the Slaad than most of what has been written about them. Exploding heads I find easy to believe.
I notice Udal the Sword erroneously attributes Simian Cult beliefs to the slaad, and that therefore the Slaad's response (and anger) is (from the perspective of my mythology, which is naturally the only one that counts) perfectly understable.
Translated into roughly mortal language, this is the conversation:
Udal the Sword: Listen, creature, we are not here to harm you—we merely seek the Cosmic Door, through which we may see all the many planes briefly align! Surely you must know of it?
Slaad: How can you have surety of anything?
Udal: Er, yes . . . But listen! I know something of you slaads. You seek to find a path into a greater reality and escape the prison of the known, do you not? If you help us find the Cosmic Door, you serve your own ends, too!
Slaad: What you have heard I choose to believe is false. What I hear from you sounds like heresy and foolishness. I choose not to believe this.
And this is what the slaad heard:
Udal the Sword: Obey me and we won't harm you. I want something from you blah blah blah blah blah and this must be true.
Slaad: When everything changes, how can you have surety of anything much less the contents of my mind?
Udal: Obey me. What I say is true. Blah blah blah blah something about there being more to reality blah blah blah help us get out to the more reality.
Slaad: You shouldn't listen to those deluded imaginations tainted by those that desire order where there is none. There is no reality on a higher existence. What a bunch of drivel. There is no reality except what you see. There is no outside creator, no flying pasta god, no higher order that makes all of this make sense. It just doesn't make sense period.
I think I'd add the following to the skill challenge:
Knowledge: On a successful knowledge skill check the player entertains the slaad with a discussion of ideas that are new to the slaad, while being careful not to assert the superiority or certainty his beliefs compared to any others. This leaves the slaad in a better disposition toward the players, and charisma based checks for the remainder of the encounter have a +2 circumstance bonus. Failure means the Slaad finds the players ideas dull, unimaginative, replusive, or else presented in a way that is too pushy or too confident. Only one Knowledge check can be attempted during the skill challenge.
Of course, I find it rather ridiculous to include the Slaad in your cosmology but not Chaotic Neutral, but that's 4e for you. If there as a more reasonable alignment system, Chaotic beings ought to get a +4 bonus on their skill checks to persuade a slaad while lawful ones would suffer a -4 penalty.