Are Inkscapes SVG documents valid SVG?
Yes. Inkscape does not yet support all features of SVG, but all files it generates are valid SVG (with the partial and temporary exception of flowed text, see below). All standard-conformant SVG renderers show them the same as in Inkscape. If they do not, it’s a bug. If this bug is in Inkscape, we will fix it (especially if you help us by reporting it!).