There seem to be two different possible questions here,
1) What should I do to combine vector and raster graphics to make a good quality print.
2) How can I maintain raster image quality with Inkscape.
For the second possible question the answer would be a purely academic dissertation on the best possible method for turning a screw with a hammer.
Inkscape is primarily concerned with editing vector graphics for which resolution has no real meaning, and as such doesn't have strong tools available to handle raster issues such as pixel density.
If this is the question which was intended this post should not be accepted as the answer.
For the first possible question my suggestion would be to import your vector graphics into Photoshop instead of the other way around. Photoshop isn't the best tool around for vector graphics, but I promise you that it's way better at curves than Inkscape is at handling pixels.
When you import the .SVG into Photoshop it open a dialog which will allow you to open the document at what ever size/resolution will match the raster photo, perhaps scaling it up or down a bit to fit (best to get this as close to correct as possible at this stage).
Now you can easily alter the document's properties to whatever settings you feel are suited to the output you intend ( typically 72dpi for Web, 300-600dpi for print), being careful of course to lock the Height, Width and DPI together to avoid re-sampling, unless it's absolutely required, in which case you will won't be trying to do so in a piece of software which is built from the ground up to output curves instead of pixels.