Yes! If it is for USPS then all label sizes are supported.
If it is for a different carrier than USPS, such as FedEx or UPS, only the 4x8 size labels will include the logo, which will print at the top.
You can use any logo in jpg, png, or gif format. The system will automatically resize the logo to fit. Go to Settings> Logo Upload. For more details visit the Help Center article: Add a Logo to your Shipping Labels, Packing Slips, Commercial Invoices and Tracking Status Page.