Warpath with the node apocalypse whirl which grant warpath the void tag does not function as a void skill with kills. At least it does not give the inspiration buff from sentinel idols with the affix “chance to gain inspiration on kills with void skills”.
A similar issue was reportet years ago in the post linked below where Hackaloken confirmed it as a bug.
https://forum.lastepoch.com/t/sentinel-idol-inspiration-on-kills-with-void-skills/25056