I'd say yes.

Even though the description of Consume Life doesn't mention anything in that regard, the effect of the ability is very similar to the Death Knell spell, which has an [evil] descriptor, and casting evil spells is considered to be an evil act unless specified otherwise (compare it to, for example, Infernal Healing which specifically states that it does not have a long-term effect on creature's alignment).

From Descriptors, under "Additional Information on the Evil Descriptor"

Casting an evil spell is an evil act, but for most characters simply casting such a spell once isn’t enough to change her alignment; this only occurs if the spell is used for a truly abhorrent act, or if the caster established a pattern of casting evil spells over a long period. A wizard who uses animate dead to create guardians for defenseless people won’t turn evil, but he will if he does it over and over again. The GM decides whether the character’s alignment changes, but typically casting two evil spells is enough to turn a good creature nongood, and three or more evils spells move the caster from nongood to evil.

No, in Pathfinder Society organized play, Consume Life is not an evil act.

Originally I'd say yes.

Even though the description of Consume Life doesn't mention anything in that regard, the effect of the ability is very similar to the Death Knell spell, which has an [evil] descriptor, and casting evil spells is considered to be an evil act.

From Descriptors, under "Additional Information on the Evil Descriptor"

Casting an evil spell is an evil act, but for most characters simply casting such a spell once isn’t enough to change her alignment; this only occurs if the spell is used for a truly abhorrent act, or if the caster established a pattern of casting evil spells over a long period. The premise of the answer is as follows:

0. Killing a helpless enemy is not an evil act in itself, as answered in the linked question.
1. There is no exhaustive list of "evil acts" in Pathfinder, and, in fact, there cannot possibly be one by the very nature of the game, so we have to extrapolate in many cases.
2. Consume Life special ability is extremely similar to Death Knell spell: it targets a creature below 0 HP, it draws its life force out, it instantly kills the target, and it benefits the user (albeit in slightly different ways).
3. Death Knell is an evil spell and says so in the descriptor.
4. Casting evil spells is a known evil act that will change your alignment over time.

Therefore, using this ability should count as an evil act.

Further, this forum post by Jacob James (Creative Director at Paizo) re Infernal Healing spell use specifically says that it is entirely up to GM to decide how long does it take for character to change alignment, be it one, ten or thousand castings.

However.

There is a rule that I originally missed that renders the whole comparison moot. There is a specific exemption for Pathfinder Society saying that casting spells with [evil] descriptor is not an evil act in itself. So, given this, casting Death Knell, and, by extension, using Consume Life is not an evil act.