There are walkons and sim signed players.. Make sure we are talking about the same things.
On will have a scholarship and one will not.
Here is what the guide says about auto signing :
Human coached teams will now auto-sign players after recruiting ends to get to 3 openings or less. So, if a team has 5 openings, they would auto-sign 2 players. The auto-sign logic at the end of recruiting will only sign guys to teams at their projected level. That means teams won't get lucky with a leftover from a higher division, and also won't get stuck with a guy from a lower division.
So yes.. You can have 3 walkons only.