When I have defined an ArcGIS Server service, and invoke the service (the url ends with '/mapserver') in a webmap in AOL, I can see that it reflects the symbology of the service.
However, when I invoke the layer directly (service url ends with 'mapserver/0') I find that the symbology is different from the service. Point layers are smaller than the service url, line layers are reduced to black lines compared to the service layer.
Furthermore, Layer urls ((service url ends with 'mapserver/0')) cannot be relocated below a service url layer ((service url ends with 'mapserver') in the layerlist in an AOL webmap, which influnces the rendering order.
With regard to your first question about symbology, both URLs should be honoring the renderer set at the layer (/0) level. Is the service that you are adding public, and if so would you be able to share the URL here? I'm wondering if there are any cache settings that may be influencing the display.
In reference to the second question, layer order of map services and layers can now be rearranged in Map Viewer Beta.
Hope this helps,