I've reread the rote spell section, and right now it seems to me like there would need to be a roll.
You still need to make a Discipline roll to target the spell, however; there’s just no chance of accidental failure.
So basically
I use a +6 rote
I roll discipline, no matter my roll, the spell goes off.
Now, several possibilities:
A) the target gets to "dodge" the maneuver with an appropriate skill, basically saying that it needs to defend against the discipline roll. If that fails the maneuver hits with full force, and the effect is determined by comparing full maneuver shifts to the defense roll.
B) basically the same as above, but the discipline roll limits the shifts that can be brought to effect, so if my discipline roll is +5 only 5 off my 6 shifts count when it comes to determine effect.
For completeness' sake:
C) target gets to dodge, AND failing that gets to defend against the shifts of power <- I'd rule this one out. since it would mean two defence rolls against rotes where there would be only one against a normal spell.
Personally I'm in favour of Version A, since attacks basically work the same way. The discipline roll does not reduce the Weapon rating of the spell, so IF it its, it hits with full force.