I agree with Dano. Roux works perfectly in some applications but is disastrous in others.
As far as detracting flavors is concerned... to a point, but no where near as much as something like cream. I find cream masks flavors in a huge way.
If you're looking to prevent the delicate raspberry flavor from becoming obscured, I'd go with arrowroot, as previously mentioned. Or, if the sauce is stock based, you might be able to augment the collagen in the stock with a little gelatin.
Also, since raspberries are so expensive and delicately flavored a lot of commercial jam makers bump up the flavor with a little lemon juice. You might want to try adding a little. Not much, just enough to give it a slightly brighter profile.
How about making your raspberry sauce into a foam?
