Yes! Although Site Monitoring was designed for automated uploads, you can still manually upload your own files.
First of all, make sure you have a monitoring node. You cannot upload into the first area you open (e.g. Campus, Building, etc). You will need to click "Add new" and then under type, select "Monitoring Node." Monitoring nodes have a zig zag beside their name.
Click into the monitoring node and simply drag and drop your .pcap (or .cap or .pcapng) file into the Files section (see the red box in the image below). Wait a moment, and it will upload and process.
Note: You need to own the site or have it shared with "Full Access" to upload a file. You cannot upload files if the site is shared in view only mode.