The answer is yes.. in the right setup it can be accessed.. however this is not guaranteed in all setups or circumstances.
See AirPort Disk - Remote Access (3 Methods)
If you cannot setup the TC as the main router.. with the public IP address on the WAN interface, it is unlikely to work.
You will only get access using a Mac.. Apple offers no methods for windows or iOS devices.
3rd party apps might work but can also be problematic as apple seem to be deliberately working on making remote connection hard outside of their fixed methods.
If remote access is a key part of what you are buying the TC for.. don't!!
Buy a WD MyCloud or similar true NAS, that has excellent remote access applications for all types of devices. Get a router if you need one as a separate item.