No. AE does not use extra channels in PSDs. It will use the Alpha channel, if a PSD is imported as a flattened image, but never Depth, ObjectIDs etc. You need to render those separately or resort to OpenEXR, RLA, RPF and IFF files, for whicxh you then have effects in the 3D category to extract the extra channels.
Thanks for the quick reply. I'll give it a go as OpenEXR.
Alpha channels that are applied as transparency in PSD files are of course handled automatically.
Non-transparent alpha channels (ie, selections saved as channels) can't be directly extracted in AE, as far as I know.
File a feature request if you would like to have this feature in AE.
As for the other question, you mean a depth map created by which application? PS 3D itself? In that case, yes, you get the grayscale map if Depth Map is the render mode in the PS 3D layer and you can use it as a luma matte for any layer in AE.