Sure, but I’d wonder why they would choose only to work within such a tiny constricting paradigm. 
It’s like staying in the world’s classiest hotel with anything you want available from a team of specialist chefs, and insisting everything you order is based on eggs… I mean yeah maybe once or twice, but sooner or later a meal without eggs in would surely start to look damned appealing?
Even if that’s your ancestral heritage, there are other spirits out there who pre-date and transcend that worldview.
Depends how you define “dark” - as “malicious and evil” or “not in the Bible.” 
If the latter, pretty much anything except prayer is going against their beliefs for some people, if they’re Catholic or Orthodox the prison system releases considerably and you have saints & angels, and there’s always the option to check out of the whole problem and directly channel Love & healing energy yourself, and use direct magick.
Have you read The Kybalion? You might find it useful.
The Kybalion PDF, archived link (we don’t trade PDFs on here as a general rule but this one is okay, the text is out of copyright and the edition was given for download from the site that created it).
I’d feel weird asking an overtly “demonic” being to assist someone for whom I knew the idea of demons was anathema, it just seems disrespectful, like hiding meat in a vegetarian’s food and then being smug when they compliment you on your cooking.
While it might feel satisfying if the person is annoying enough, it attacks your own integrity more than it harms them. If you align your work with their values, you can be sure that you’re genuinely helping them, and not just point-scoring (not accusing you of that, just something I think is important when helping people with strongly-held religious beliefs). 