There a several places the library would need to be updated depending on which parts you are using.
Things like around line 517 in InitializeTooltip(tooltip, key)
Code:
local backdrop = GameTooltip:GetBackdrop()
would be followed by
Code:
if not tooltip.SetBackdrop then
Mixin(tooltip, BackdropTemplateMixin)
end
tooltip:SetBackdrop(backdrop)