The passive past life druid feat is as follows:
You were a Druid in a past life. You occasionally find yourself gazing at the stars and get sentimental around mistletoe. Each time you acquire this feat your summoned creatures, charmed minions, and hirelings gain +2 to all ability scores. This feat can be stacked up to three times.
Granting +2 and eventually +6 to all ability scores for charmed minions will harm one's ability to keep enemies under the influence of charm type spells by increasing the monsters saves. While initial save success won't be affected, the periodic save to maintain control will be easier for the enemy to make. I'm now reticent to TR into the Druid class.
This drawback of past life: druid could be remedied by causing the feat to no longer affect charmed/dominated etc. minions, while still affecting hirelings and summons.
Better yet, the minion's saves against the augmenter's spells could be made to not increase, or for the fortitude and will save of charmed minions to decrease in tandem with the saves granted by the stat increases.
Apologies if I have misunderstood how augmented summon feats work and that in fact the minion's saves against the augmenter's spells do not increase. If this is the case I would request that this be noted in the feats' descriptions. Judging by recent forum posts and ddowiki it's not just me who assumes (there's every reason to from the description!) that these feats increase the chance for enemies to break free from charm-type spells.