Sure it's limited. Not by the software but by some sort of technical limitation. A lot of it is going to depending upon the hosting computer's hardware and O/S and then bandwidth. So, lag is going to be close to linear to the number of clients. If you ignore lag, I suspect a practical limit is going to be somewhere around 30-40 cleints before you get too much contention.
Note, I would expect lag with 30-40 clients to be unplayable. But, you would expect a relatively stable connection.