What speed are these lenses? In all likelihood, you need to zoom in more as a result of the small rear aperture on these lenses. Once you get below f 2.8 any adapter out there will show its limitations. In essence, unless you have very good light, the max rear aperture of an f 4.0 will vignette as you zoom in...meaning you need more light, or more zoom on the DVX. What you are seeing is not really hot-spotting, but rather vignetting. The f 2.8 lenses I've tested work perfectly at all zoom levels.
Keep in mind that the diffuser on the Brevis is a fair bit larger than an actual 35mm frame. This permits a larger frame with fast lenses, but requires more zoom in with slow lenses...and the usable image frame will shrink as you push higher f stops with slow lenses. The DVX zoom for an f 1.4 50mm would therefore change with a slower lense. This is not unique to the Brevis, and is likely much worse (if you could measure actual frame size) with other adapters out there.