Yes, I am able to open the file in acad and it appears that the data came over correctly with the exception of some dimensions. They appear to not be connected to the SU file so are displaying the paperspace diimension.
The image that LO added is essentially the raster render of the SketchUp view. This can be included but does not need to be included to your consultants. If you set the SketchUp viewport to Vector and not using the “Export raster-rendered SketchUp models as Hybrid-rendered” checkbox it will export just the linework and not create an image.
The scale is set by selecting the SketchUp model viewport, and setting the scale from the SketchUp model panel. This scale will be passed to AutoCad as a scaled viewport.
Using the setting you used this time, the model is correctly exported to the model space at 1:1 so your consultants will not need to scale it up using these options.
Without seeing your file I am guessing that the style you are using is why the background may be too dark. You can turn off the background via selecting the SU model and unchecking the background from the SketchUp model panel, Style tab.
The screen shot your engineer sent sounds correct. The missing image .png is seen accross the background. This can be unloaded within acad but is not needed.
If possibile could you send me or SketchUp support the .layout file?