Can Harpie Dancer re-summon a monster on the turn it was returned to the hand?
Is this move legal?

Yes it is.
In no place in Harpie Dancer's effect indicates that you can't summon the monster you returned to hand (emphasis mine):

You can target 1 WIND monster you control; return it to the hand, then you can Normal Summon 1 WIND monster. You can only use this effect of &quot;Harpie Dancer&quot; once per turn. This card's name becomes &quot;Harpie Lady&quot; while on the field or in the GY.

As we can see the only requirements you mus fulfill are (1) target a WIND monster to return and that (2) the monster you Normal Summon is also WIND.... Pay special attention to the &quot;you can&quot;... that means you may chose not to Normal Summon after returning.
In fact, doing this is one of the strengths of her effect, allowing you to return/re-summon even if you only have one other monster (so you can trigger Harpies' Hunting Ground, Divine Wind of Mist Valley, etc.).
What's more, you can even return and re-summon Harpie Dancer herself... or just return her and summon nothing...
Remember that, when a card returns to the hand, it &quot;resets&quot; and loses all memory of who it was on the field (similar to MTG I recall??), so for the purposes of the resolution, the effect doesn't care who that card is, as long as the requirements are met (it is a WIND monster that you can Normal Summon).
As a side note, I'm a main Harpie player :)