I have never heard anything one way or the other about soil from around a cedar tree. All you can do is give it a try and hope all goes well.
Good luck!!!
The main thing I would worry about is what effect the dropping leaves ( I think with cedar they are leaves and not needles) might have on the soil pH as they decay. I've read that they drop the soil pH and make it more acidic, which would be great for blueberries, but then I've read that this drop in pH is only temporary while the leaves are decomposing. Once decay is finished, the pH effect moves back to neutral. I don't know how correct this is. I'd think you would be wise to test the pH anyway.
I guess the other thing I'd look at is how much non-decayed organic matter there is in the soil. While it is decaying, it will tie up some of the available nitrogen in the soil. Once it is decayed, that nitrogen is again available.
I seldom see much of anything growing under cedars, but then cedars don't let much daylight under there. I think this lack of daylight is more the cause of things not growing under there than anything else.
So I would probably try to avoid mixing a lot of the undecayed organic material that is in the top layer, check the pH, and use it.
I'm not an "expert" on this, just giving my opinion. I'll be interested in what others say.