I read the sentence to say that the penalty should impact only if your followers are living; undead followers, which should be available under Leadership too, would not be diminished, but bolstered. Effectively 2 sets of Undead (say, Necropolitan) followers at +2. Or are you saying that Leadership can't attract intelligent Undead followers/Cohorts, so would be automatically diminished?
My stated plan has been to have Necropolitan (+0 LA), Magic Blooded (+0 LA), Lesser Aasimar (+0 LA) Cohorts and followers. For those starting above 2nd level, I was planning on having Draconic Templated (+1 LA) Cohorts and Followers.
[Edit] Upon consideration, the Half Nymph Template (DR 313, p95, +2 LA) instead of the Draconic Template looks rather promising for my PC and any Cohorts (and Followers who begin play at 6th or higher); +2 to Dex, Int and Wis, +4 to Cha, minor version of Nymph's Blinding Beauty (causes shaken in Humanoids). Loses +2 to str, but that's not necessarily too bad, and allows reflow of the PB chars' stats around it (dex & wis, mostly)...
My PC and Cohorts would have any un-bought-off LA on the Marshal/Legendary Leader side of the Gestalt, so PC is at full, Cohorts at LA 1 until 9th.[/Edit]
Having undead followers is why I have L. of the Dead on my char and my Cohorts over 6th level; it boosts Turn resistance for the character, and also bolsters Turn Resistance for 'Undead allies within 30 feet...'