Will Huntress work with 3rd party AVs? 

The Huntress Agent itself will run alongside any other security products (sometimes you may need to add Huntress to your AV exclusion list [whitelist]). 

However, you cannot utilize our Managed Microsoft Defender AV features. 

Microsoft Defender disables itself when another AV is installed to prevent conflicts. Microsoft Defender has some functions that you can re-enable, but it won't be fully functional. All 3rd party AVs need to be uninstalled for Microsoft Defender to work at full capacity.