qobofusDifference is significant.
"I will give to her the axe" is not the same as "I will give her to the axe". The latter implies that you will give said woman to said axe which is nonsense. In other examples this could lead to miscommunication of a massive scale.
They are quite different, so the question is do we let -a be used for only one of these or do we let -a be used for both?
Your example actually works out okay; "Zu'u fen ofana mek hahkun." The possible interpretations would be "I will give (to) her the axe" and "I will (to) give her the axe." Since the latter doesn't make sense we know the former is the correct translation. In the same way we know "Rok funta koraav" is "He failed to see" and not "He to failed see." As Hiith pointed out it would be even better to just say "Zu'u fen ofan mek hahkun," "I will give her the axe."
Let's see if we can come up with examples where having -a mean both would cause serious problems. Remember that it would only be used when "to" directly precedes or follows the verb.