Sniperbots need a func_tfbot_hint, so they know where to stand and aim. Engineer-bots, on the other hand, use regular point entities (bot_hint_sentryspot, bot_hint_engineer_nest and bot_hint_teleporter_exit).
If you don't have said bunch of entities on your map, neither bot is gonna do anything (especially Engineer, he really doesn't wanna do anything if the map doesn't have those entities for him)