This question has come up:
Do targets get a surprise reaction during a surprise round, where reaction is things like Dodge and Parry?
In the rulebook on page 235, it states that "He can do nothing but stand there dumbfounded'. I seem to remember that dodge and parry were the exception to this.
The problem is, there are several Squad Mode abilities that allow you to take actions in the place of reactions. This could, for example, allow a character to actually get a shot off during a surprise round.
Surprised character: Reactions or not?