If you are going to use UE with pwS2, it is HIGHLY recommended that you disable the Ambient Occlusion, AO for short, in one or the other. Do not have it active for both and here is why.
Uberenvironment is a type of lighting for DS. pwSurface2 is a surface shader. Both pwSurface and Uberenvironment use AO but they both do it differently. And its the AO that is clashing. UE has a single control for AO, which some people prefer, that affects the entire scene all at once. pwS2 being a surface shader applies AO only to the surface of which pwS2 is applied to. Please note, in DS3 & 4 you can use the surface selection tool to right click any surface and tell it to mass select all surfaces using pwS2 or whatever surface shader you are using. Though there is no global control for AO with pwS2, you can have far greater control over how it is applied. Two examples would be colour and just how much AO is used. pwS2 allows you to define the colour of your AO so if can better reflect the surface its being used on without affecting the strength of which it is applied. You can also determine the amount of AO used in different parts of your scene. If you render a lot of scenes with hair and raytraced shadows, you can leave the amount of AO in the hair to be lowe then in other parts of the scene. I tend to do that mainly via the quality level controls that come with pwS2 though the overall strength of AO can be used to affect that as well.
I personally do not use UE at all. As an avid pwS2 user I prefer the standard DS lights combined with pwS2 on all my surfaces. It is a lot harder to fake Global Illumination that way I will admit and though I have in not perfected it, I know it can still be done reletively well. From my own personal tests, I find pwS2 used with standard DS lighting renders a lot faster than UE and with equal quality.
Please feel free to check out my gallery here to see examples of pwS2 in use - http://mattymanx.deviantart.com/gallery/