JPEG core with NiosII

Yes, you can create your interface component in VHDL and use it in your SOPC Builder system. The main purpose of that component is to bridge your camera interface signals to the system interconnect fabric. You would still have to connect the camera signals in Quartus via pin assignments.

You shouldn't have to understand the VHDL that the DMA is written in since the component is completed for you.

PIOs are simply memory mapped registers so that's why you couldn't use them for your interface. I recommend that you stuff the data from your camera interface into a small FIFO then map the read side of the FIFO to the system interconnect fabric. If you search the forum I think you'll find something similar to this in the IP section.