With the current laws against religious and cultural discrimination, I'd be very surprised to see anyone's religion being a particular benefit to his/her career advancement.
If anything, in a secular workplace, any seeming favoritism as a result one person having the same religion as another (e.g. I am a member my boss's church) is a red flag. My experience as a manager has been that others in management actually take extra steps to avoid anything that might be misconstrued as favoritism - even to the point of discrimination.
Example: My former director was a Jehova's Witness. I hired two individuals from his church over a period of three years. Despite the fact that both of these individuals were extremely competent and hard working, I could not always reward or recognize their contributions as frequently or to the same degree as I might other individuals who were not connected to my director in the same way due to complaints of alleged favoritism. It was ridiculous since I could care less what my employee's religious affiliation was - I rewarded strictly on merit, but, sadly, such was the case.
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