His comment about creating hidden identities was related to NMDC and it's different with ADC. I'm not totally sure that why the chat history bot has such identity but I'd assume that it makes the hub-side implementation easier (extending/scripting ADCH++ has been implemented in a really awkward way).
The assumption should still be that hidden identities are totally invisible to the users so this kind of "issues" shouldn't affect the way how hub-side features are implemented. If you try DC++, you'll notice that it will totally ignore hidden users in the total user count.