This is the first I heard of it. My parade is canceled due to rain. Darn it, I guess the surpriser ability is too good to be true.
You are correct. The surpriser ability does nothing.
The ability makes a check against the counter surprise value of the opposing force. A single leaderless militia has three times the counter surprise value as the surpriser ability, making it mathematically impossible to surprise a barn door. But Captain_Orso pointed this all out back in 2012...
I increased the chance to surprise to 100% just to see what it did. It increased the initiative value of all elements by 50%.
The ability should really be removed if it does nothing. Especially since it seems so powerful.