Without luminance correction Encore will definitely scale the AVI/MOV to 16-235. I added in a lossless 0-255 AVI and the output was 16-235. What happens if your input is already properly scaled? Is Encore smart enough to not do anything or will it still scale it ?

By the way my other tests have shown that adding video effects in Premiere Pro will automatically do a highlight compression for superwhites, whether you want that or not.