Not exactly. I've never been at any foundry in recent years that didn't have a prescribed pad ring that you were required to use. That "prescribed" can be an issue... particularly leakage with sensitive analog inputs. I did manage once to break the rules at X-FAB and get ESD diodes back to back to ground for an RFID tag chip whose input was at ground potential.
(I also like to spin my own device structures/layouts, as I did as a kid, but no foundry will let me anymore :-(
Here's the basic skinny... the production cost of a wafer is a constant (for a given number of process layers).
The more chips I can get on that wafer means each individual chip cost is lower, and there's more potential profit to be made. ...Jim Thompson