Visual inspection of both tractography and the underlying tensor glyphs is recommended. For tensor glyphs, use the Volumes module to enable “Glyphs on Slices Display”:
As far as validation, that’s a complicated subject. Various groups have done ex-vivo work with tracers and comparison of histologically-derived white matter to tractography. Here are two papers that come to mind immediately, I’m sure you can find more by looking at the citations for these (and similar keywords):