you're using the HPB_bot SOURCE CODE to make your own bot, not the official HPB_bot release... so this is a coding question
Actually all the HL bots out here are more or less based on the HPB_bot, you know
Anyway... is there a menu selection in your mod ? (to join a class, to choose a skin, whatever)
Maybe the bots are stuck in this menu that's why they don't appear...
Check if their entity has the EF_NODRAW flag set.