I have no doubt running the Hoprocket in its normal direction without a pump will provide some filtering. I just want to be clear that running it in the opposite direction with a pump "pulling" the wort will compress the hops to the point that the wort can hardly get past the filter bed. The hops are compressed so much that they're literally like a brick. It may be hard to tell in this picture but the bottom of the hopsack is perfectly flat and you can see the hole marks from the screen.
Absolutely - and adding the bag into the mix is going to make it a mix of both depth and barrier filtration. It'll be most effective.
But, addressing the OP's question rather than your particular technique - the bag isn't at all necessary in order to have the hop rocket serve as both an effective hopback for flavour/aroma infusion AND as a a perfectly effective trub and hop filter to go before a plate chiller. Used as its designed, it does both eminently well. Bag not needed and pump not needed.
Hoprocket operating under gravity and oriented as it was designed.
Nicely compacted plug of hop that the wort had to filter through - it comes out more than acceptably clean. I have no issues running it through my plate chiller with no whirlpool or post boil rest. Nor do I have issue with the level of clarity for brewing quality purposes - and I care about cast wort clarity.
So IMO - the answer to the OP's original question is a simple YES. The hop Rocket can be used as a filter to go before your plate chiller.