A couple big disclaimers:
I only tested my Nexus 6 with Verizon briefly and that was a week ago, so this may no longer work.
I currently have my Verizon service officially suspended WITHOUT BILLING, since I figured I could get the device much quicker by giving TMobile a whirl---I was right.
However, there is no way I will voluntarily give up Unlimited Data on Big Red.
Again, if you try this, proceed with caution:
If You have Root Explorer, go into the system files and edit the Build.prop file
add this line at the very end/bottom:
net.tethering.noprovisioning=true
Save changes and reboot. Also, Root explorer should automatically backup your original build.prop file, but make sure you have a backup regardless.
While I can't find the original thread at XDA, I want to make it clear that I don't deserve any credit for this.
Edit: Think I found it. Refer to Post #43:
Nexus 6 on Verizon - what works and what doe… - Pg. 5 | Nexus 6 | XDA Forums
Also:
http://forums.androidcentral.com/droid-maxx-rooting-roms-hacks/415581-native-tether-any-version.html
This Last thread appears to be primarily for Sprint Users but it may provide helpful info if the previous advice no longer works.
Sprint Nexus 6 Wifi Tethering *root* UPDATED… | Nexus 6 | XDA Forums
Again, not trying to thread crap, Foxfi is good too.