Dembski isn't all of intellegent design, perhaps about 25% though.
Surely more than enough to qualify him as an expert on the question of how Intelligent Design is related to religion.
Which reminds me, have I mentioned what Dembski reportedly said on the topic?
"Intelligent design is just the Logos theology of John's Gospel restated in the idiom of information theory," William Dembski, one of the movement's chief proponents, said in a 1999 interview in Touchstone, a Christian magazine that Forrest cited in her testimony.[emphasis added]
The only open question is whether or not Dembski was telling the truth when he said that (I discount the possibility that the quote is inaccurate, since the defense surely would have presented rebuttal evidence to that effect were it case, which they haven't.)
As for Dembski's truthfulness about the faith-based origins of ID, all I can say is that while he arguably might have a motive to suppress the connection (to get the subject into schools), I can think of no corresponding reason for him to claim ID has faith-based origins if that weren't the case. What, pray tell, would he gain by claiming that if it were not true?