Hi Logan,
UPS Collect is not supported via the API, however, you can ship using your customer’s UPS or FedEx Account number via 3rd Party billing as a package option. FedEx Ground Collect is supported via the API, however, this would be a situation where you do not have the customer’s FedEx account number. Rather your customer has notified FedEx that you are allowed to ship on their account FedEx Ground collect only.
To Bill Shipping Fees on a Customer’s Account, please see this Knowledge Base article: