Redwolf passive skill: What are the chances for this passive to execute by skill level?

Looking through a number of forum posts, Red Wolf will always look for up to two targets to savage when you crit. It's not a chance - the skill is just worded poorly.

TL;DR: Between the two skills you're looking at, Rage Retaliation is more reliable than Red Wolf. However, your best bet for picking a skill is to try fully investing in each and doing a respec if you don't like the results.

Red Wolf is not reliable because it hits the two targets closest to your character model, not your target. If you are using a long reach melee weapon, you will find that you rarely proc Red Wolf because you are standing too far from your target. This is even more true when using ranged weapons, which will only savage enemies standing right beside you when you shoot from a relatively long range. Some players have claimed that even standing close they sometimes do not proc Red Wolf, possibly because hitboxes are used instead of a distance check. It also doesn't help that Red Wolf seems to have an internal cooldown, meaning it won't proc every crit depending on your attack speed.

For best results with Red Wolf you need a short-ranged melee weapon. Then you should see two enemies being savaged every time you crit. With any longer ranged weapons you will have to stand closer to your target.

Given usability issues with Red Wolf, you will likely see better results pumping points into Rage Retaliation. Rage Retaliation:

• Has no internal cooldown with 11 points invested.
• Functions per monster, so deals much more damage against groups.
• Scales with weapon damage instead of player level, which is better if you gear up.
• The scaling boosts massively when investing from 11 to 15 points (+40% weapon dps), so it rewards you for investment.
• Has a more reliable distance for procs.
• Will proc as often as Red Wolf because a Berserker, depending on your playstyle, roughly takes damage as often as they dish it out. This is especially true for life-steal focused builds.

Rage Retaliation will only feel weak:

• Against mobs with very slow attack speeds, especially some bosses.
• If you don't plan on taking damage.

If the above two points are a deal-breaker for you, then don't bother with Rage Retaliation. Also note that neither skill is at maximum effectiveness against a single mob.

Follow-up forum post, and original forum post.