It is possible to trade into a Hilton via RCI.
Couple of pro and cons:
Points required are less via RCI. A 2 BR red season week (you use RCI seasons not HGVC seasons). So a Platinum week could be obtained using a 4800 points via RCI and it could cost 7000 or more for the same unit via HGVC.
You pay an exchange fee that is four times higher than HGVC charges ($199 vs $49). But it is a trade off as the points are far less.
You can only book into HGVC resorts via RCI in the same 9 month rule that you have via HGVC open season. Even though units are often available in RCI for longer that the 9 month out.
And once you stay at a resort, RCIs 1 in 4 year rule kicks in and you can not return to the resort for another 4 years VIA RCI.
(I was wondering if the 1-in-4 rule would kick-in using the HGVC-RCI portal: Bummer. 
But like you said, you can always use your HGVC points if you want to go back: i.e. 57th ST. :whoopie: ) You could always go back via HGVC.
So how has that worked for me...
In the last 3 years I have booked into a 3 HGVC units, via RCI HGVC portal, or via another RCI account that I deposit non-HGVC weeks into.
I booked a 2 BR at Kingsland, used my non HGVC RCI account, and booked it for a week that had a $350 MF and paid the exchange fee. But worth far less than either the 10.5K that it have cost via HGVC directly. Even via RCI this would have been a deal.
I booked a studio at Hilton Club NYC for 2400 HGVC points via my RCI HGVC portal.
I also booked a 2 BR Thanksgiving 2013 in Waikiki. Here I used my non HGVC portal, as the HGVC portal would only allow me to book 9 months out.
It is good to take advantage of some of the bulk spacebanking that HGVC does periodically. It also stretches your points a little farther.
