If I read it correctly, you can get multiple skillups if the skillups trigger on a failed attempt, which they do for evasion, parry and guard. So it should be possible to get an evasion, parry/guard and shield skillup at the same time. Should be easy to check on a unleveled mule, so I'll report back later with the results.
Edit: confirmed it. I got evasion, parry AND shield skillups on one and the same attack.