[mack848]

You can raise for value HU, as your equity is not simply the % of the time that you improve to a winning hand. In HU pots especially, the combination of the equity of your draw + the chance you are ahead + fold equity could well be >50%.

You are correct that it is extrememy unlikely that your draw alone will give you sufficient equity to raise the turn HU. A semi-bluff raise could well be correct though – if you suspect that your opponent might fold a better hand, or that you are ahead. You need to estimate whether the cost of raising is worth it. This would need to be based upon your read of them (can they fold?), their possible holdings (TPTK or middle pair?) and the size of the pot. They will only need to fold very occasionally in a medium sized pot for a semi-bluff raise it to be +EV.