Do I need to add a bot account to a WhatsApp group

No. OpenClaw runs on your own account, so if you’re in the group, OpenClaw can see it. By default, group replies are blocked until you allow senders (groupPolicy: "allowlist").
If you want only you to be able to trigger group replies:
{
channels: {
whatsapp: {
groupPolicy: "allowlist",
groupAllowFrom: ["+15551234567"],
},
},
}