Hrm.
I took the time to painstakingly destroy a group of Kobolds and two groups of Hobgoblins using nothing but Sure Shot and couldn't replicate the non-crit. I even cast Blessing a bunch of times in case getting the bonus over 255 broke it (it still happens to the best of programmers) but it still crit.
...and then I met a group of Imps, used Sure Shot (at +254 Accuracy) on "Imp Shanker B" (one of the 300 HP ones), and it didn't crit.
The only buff it had on it was Guarded Stance, which doesn't stop crits and doesn't require a shield, but... maybe it does have one equipped? I didn't know tanky Imps were a thing, but I guess it's possible.
I guess, if you learn which of the enemies are crit-resistant, you could go in with a Petal and Sure Shot would make sure you have the Bless buff up at least half the time... the crit rate on enemies was still quite low with AoE attacks, but I usually got at least one crit with them when all enemies were up.