If you install a hack from FireFly located
here, you can quickly and easily add new Who's Online locations to your board. Basically, after installing the hack, you use it to tell the board about a new non-vBulletin page that you've added into the vBulletin system, and you tell it what to show as a description for that page in the Who's Online. With either this hack by Jakeman or the similar one by myself that I linked to in an earlier post above, the chat room is on a separate page, to FireFly's hack is perfect.
The only limitation is this doesn't actually check to see if a member really is in the chat room; it only knows that the member tried to visit that page. If the member was unsuccessful (due to permissions or whatever), he/she will still look to Who's Online as if he did get into the chat room...just as if a member tries to edit another member's post, Who's Online would show that the member is editing that post, even though the member is really seeing the no permission page. Also, if the member is browsing the board in multiple browser windows, then as soon as he goes to another location in another window, he/she will be shown as being in that location, even if he/she is still in the chat room in the first browser.
There has been mention in the past about setting up bots to stay in the chat room that would somehow be able to keep vBulletin actively and accurately notified about who is in the chat room, but all that is beyond me at this time. But if you really want to read up on that, follow the link to my hack in my first post above, and in that thread, look
here, or search this board or the one at vbulletin.com for "chat" or "chat AND integration".