I think I may have figured it out.
When referencing an enum item directly, it uses the type of that item. So above since SDKLibCall_TerminateRound doesn't have "Handle:" before it in the enum then when I use it it's reading it as an integer.
But if I use an "SDKLibCalls"-typed variable then it would read the type of the array.
Code:
new SDKLibCalls:sdkcall = SDKLibCall_TerminateRound;
SDKCall(g_hSDKCall[sdkcall], client, delay, _:reason);
So that compiles without warning. Kind of sucks that I have to tag every item as Handle though. But I'm assuming that's just Pawn's design.
EDIT: Just realized I can't tag each one as a handle because multiple arrays are using that enum.
This seems like a design flaw. It should be taking the tag of the array not the enum member. Any SM devs have anything to say about this?