Correct Sierra 10.12.5 file paths to Spotlight and SpotlightNetHelper files to be blocked with Little Snitch?
In macOS Sierra, SpotlightNetHelper was removed and the standard WebKit networking is used instead, located at /System/Library/Frameworks/WebKit.framework/Versions/A/XPCServices/com.apple.WebKit.Networking.xpc/Contents/MacOS/com.apple.WebKit.Networking.

There are various apps and processes which use this for networking, so you can't simply block it entirely without affecting those too. However you can set up a specific rule to prevent it connecting to Apple's services for Spotlight, which would prevent Spotlight using it to talk out, as shown in the first screenshot where the rule is ‘Spotlight via com.apple.WebKit.Networking’.