If I install the VAPI marketplace app in GHL, will I be able to rebill the sub-accounts for the call minutes if requested by that sub-account?

Yeah

are you talking about this app? it doesnt say anything about rebilling minutes https://cdn.discordapp.com/attachments/1392574536804864011/1393256432962502758/image.png?ex=687282ab&is=6871312b&hm=17c70bd45d9700cf67a8ab9ab72fa9b7c101e1d4dcc619e5cfe3767c45d515fd&