IMHO
No! 
There is garbage out there. If only the people releasing this would check first.
I also take the time to clean unused classes from the CSS. (If this is a 'house' stylesheet, there is nothing to lose, except byte count, if doing a
cleaning before release. If the later find they need a 'deleted' class, just replace the CSS with a fresh copy

, then clean that.) BPH stylesheets can lose over a 1000 lines, cleaning the unused ones.
Do be aware of those warnings, and get used to the
regulars like you mentioned. There will be others that crop up , that just might need attention because your device does have issues with that one.
OTOH these checks wont report valid code, that your device screws up on
eg a HR of 50% width is supposed to center, but does not on older RMSDK. You need to work around this (margin_left: 25%)