I found several threads that all ran into this same issue.
Plenty of ways to get around it.
"Computer"."OS"."PreBoot OS" = "WinPE" AND "Computer"."Inventory Server" = "CORENAME" Catches PXE booted or machines booted from CD/USB provisioning media
"Computer"."Network"."Pxeboot" = "Yes" - catches PXEBooted machines
"Computer"."Device ID" = "Unassigned" OR ("Computer"."LANDesk Management"."Agent Configuration Name" NOT EXISTS AND "Computer"."Device Name" <> "CORENAME") Catches all unassigned deviceIDs with no Agent config that aren't the core server
You can further restrict these all based off IP Address, subnets, etc etc etc
You can even filter based on which PXE Rep it PXE booted off with "Computer"."LANDesk Management"."PXE Holding Queue". "Proxy Host Name"
I'm not really sure which way is the best way to go.