Yes , you can create Custom Orders without prior adding product in the master catalog.
(Note : The product entered while creating Custom order will be a run time product and will not be saved in Master Catalog)
Steps to Create Custom Order
Step 1. Goto Orders -> Click Add Order
Step 2. Fill in all the Order related details such as :
Customer Details : This includes the billing and shipping details of the customer.
Product Details : The Product will be created run time and will be order specific.
Payment Details : All the payment related information with respect to the order, such as if the order is “Cash on Delivery /COD ” or “Prepaid”.
Step 3 : Click and your order will be created.
(Please note that Custom Order is only available in Shiprocket Lite plan and will be available in other plans in next release)