can we add ἄν in the apodisis?

οἴει τι, ἔφη, ἧττόν τι τοῦτο εἶναι αἰσχρὸν ἢ εἴ τις ἔχων μὲν ἀγρούς, ἔχων δὲ ἐργάτας οἷς ἂν ἐργάζοιτο, ἔπειτ᾽ ἐῴη τὴν ἀργοῦσαν ἀνωφέλητον εἶναι; Can we say: οἴει τι, ἔφη, ἧττόν τι τοῦτο ἂν εἶναι αἰσχρὸν ?

No. “Do you think that this is worse than [it would be] if . . .”. Not "do you think that this would be worse than [it would be] if . . . "

ἥττόν τι εἶναι αἰσχρὸν is not the apodosis of the εἰ clause. The apodosis is understood: something like ἐγίγνετο ά̀ν.

ok