You can ask all you want, the company is required by law to not discriminate based on religion in which case they will likely not be able to provide you a completely candid response. I would phrase the question more like, in your culture and respecting various religions to avoid discrimination do you make any special accommodations or is it just like use your vacation time for any religious holidays you want personally?
That is basically the same thing, but puts it in a light that communicates you trust the company is not discriminatory, but want to know if they accommodate a specific religion or not. You can also ask for examples if it helps to figure it out.
There are some that just talk anyway, but that would put them in line for a possible lawsuit. With freedom of speech in the US as an individual your beliefs are protected so long as they don't cross into bounds where things are regulated (like discrimination in the workplace, verbal assault, etc...).
If the Company asks you:
Please reference the laws regarding this here: https://www.eeoc.gov/employers/coverage_private.cfm
After that pay close attention to what they are asking, but know that you don't have to answer anything religious in nature if you don't want to. They should be volunteering information and not quizzing you on religion. If it appears like the second ask them specifically about why this is pertinent to the job and get a detailed and satisfactory answer from them. Even if they don't discriminate and make it a legal issue, if everyone is in the same religion and you aren't it might make it very undesirable to work there.