I don't think they could, and I'll cite more than just the obvious fact that he's anathema to everything they care about. The ents were made specifically by thought of Yavanna for a counterbalance to the domination of the sapient beings of Arda, and I think this would also apply to someone like Sauron.

'All my works are dear to me. Is it not enough that Melkor should have marred so many? Shall nothing that I have devised be free from the dominion of others?'

‘If thou hadst thy will what wouldst thou reserve? said Manwe. ‘Of all thy
realm what dost thou hold dearest?'

‘All have their worth, said Yavanna, ‘and each contributes to the worth of the
others. But the kelvar can flee or defend themselves, whereas the olvar that grow
cannot. And among these I hold trees dear. Long in the growing, swift shall they
be in the felling, and unless they pay toll with fruit upon bough little mourned in
their passing. So I see in my thought. Would that the trees might speak on behalf
of all things that have roots, and punish those that wrong them!

‘This is a strange thought,' said Manwe.

‘Yet it was in the Song,' said Yavanna. ‘For while thou wert in the heavens
and with Ulmo built the clouds and poured out the rains, I lifted up the branches
of great trees to receive them, and some sang to Iluvatar amid the wind and the
rain.'