Can I keep track of one specific app's sales from someone else's iTunes Connect page? I'm an iOS developer, and I just found a publisher for my app - they will sell the app with their own iTunes Connect account.

I have my own iTunes Connect account as well, and I'd like to keep track of my app's stats. My publisher says they would give me access to their iTunes Connect page, but I would be able to see their info for all of their other apps. So they suggested to use a service called Appfigures.

I'm a bit skeptical - is there really no way I can have access to the stats of one specific application in their iTunes Connect page? If not, are there more reliable services to keep track of such data?
They are correct, a user on iTunes Connect has access to all apps, no matter what their role. Obviously this is a terrible design, but Apple has never been too quick to fix design flaws in iTunes Connect.

As you mentioned appFigures has the ability to restrict a sub-user's access to individual apps. The publisher will have to set up the primary account.

I can't find official information from any of the other analytics providers that they have this capability. My App Annie account definitely does not.