A remote agent is a VICIdial agent entry without an agent screen. When VICIdial routes a call to it, the call is forwarded to the phone number or extension in the entry. One entry can take several lines at once, set by its Number of Lines.
VICIdial's install notes describe the original purpose: giving agents "a way to receive calls to whatever number they happen to be at". That is also how an AI voice bot can take calls from an existing VICIdial campaign, with no person at a screen.
VoiceOI bots run as VICIdial remote agents. VICIdial keeps your lists, campaigns and reports, the bot runs the conversation, and each outcome is written back as a disposition. The VoiceOI team does the integration steps and creates the VICIdial users and phones.