Zero investment in dodge/evasion results in 95% hitchance for the enemy unless it's reduced by external factors such as darkness, distance, burst penalty, move and shoot penalty etc (flat amount).
Basic precision is 70% - the enemy has the same attack skill vs your defense skill. It can be reduced by 60% max if your defense is twice as high. So if enemy has 140 melee skill, then you'd need 280 in dodge to bring his hitchance down to 10% which is lowest possible. That's why the arena boss is so hard to hit unless stunned, incapped, immobilized or have his exceptionally high dodge negated by any other means. For the same reason are traps and sledgehammer Pummel so effective against him.
Beware that both dodge and evasion (along with stealth and MP) are reduced by armor penalty (the same amount in %), so having 280 (or any) points in dodge is pointless for a 80% armor penalty character, leaving only 56 effective points as defense. I usually don't bother rasing dodge at all if late game I can't have 150+ effective points together with tabbis/syphoner armor. Otherwise dangerous enemies will hit regardless. One exception is the Uncanny Dodge feat that works well even with little dodge.
Evasion on the other hand is always useful even with medicore values because in worst case, if it doesn't help much to avoid ranged attacks at least it always reduces AoE damage to some degree and anything is welcome against one-hit killers like high tier frag grenades/mines.