I am really enjoying using mogrts to streamline mograph processes with the editors. So far this is one of my only struggles. I am not 100% sure if there's a workaround but I thought I'd ask before submitting a feature request.
When I have a layer in AE with a blending mode selected other than "Normal", i.e. "Add", that blending operation doesn't follow into Premiere Pro with the Mogrt. It would display well if I have a background layer below the blended graphic but not if there isn't anything below it other than the video track in Premiere. You may be able to set the blending mode of the whole mogrt but not keep the appearance you set in AE. See attached example files. They include an AE project where the mogrt was created, the resulting .mogrt file and a PP project where the problem is shown.