Short Answer
The only ID I could get working was a combination of the class and unique ID.
#IfWinActive ahk_class Windows.UI.Core.CoreWindow ahk_exe Explorer.EXE
I found them by activating AHK's Window Spy and squinting at it while the Task View was open.
This doesn't conflict with the start menu search, file explorer, or other system contexts I've tested.
A Useful Way to Navigate Task View
The following is not directly relevant, but there aren't many posts on Task View and AHK, so this may be helpful to have here.
I'm using this ID for context-sensitive hotkeys to navigate in Task Switcher without moving my hand (h,j,k,l instead of arrow keys) and open or close windows. If you're curious, this is the script:
F4::
run, "C:\Users\Default\AppData\Roaming\Microsoft\Internet Explorer\Quick Launch\Window Switcher.lnk"
; this was originally written for Win 8.1, but it still works in Win 10 despite the
; shortcut being invisible in File Explorer
return
#IfWinActive ahk_class Windows.UI.Core.CoreWindow ahk_exe Explorer.EXE
l::Send, {Right}
h::Send, {Left}
j::Send, {Down}
k::Send, {Up}
o::Enter
x::Delete
return
I use it in combination with this little gem for switching to the most recent window without any GUI splash (simpler AHK solutions I tried had glitches, and I left out the menu part of this script). Task View is great, but often you just need to get to your last window without any fuss.