I asked this exact question about tidy errors in VIM on Syntastic's issue tracker.
Add to your vimrc:
let g:syntastic_html_tidy_ignore_errors=['proprietary attribute "ng-']
This will get rid of errors for any attributes prepended with ng-
, leaving errors for all other proprietary attributes.
If you have a namespace prefix for your own directives, you can add it to this list as well.
let g:syntastic_html_tidy_ignore_errors=[
\'proprietary attribute "ng-',
\'proprietary attribute "pdk-'
\]