I'm not sure it matters what the erased state is as long as the "erased" value is defined and handled correctly.
Also keep in mind that some flash chips may not support flipping single bits inside of bytes or flipping individual bytes etc and warn against it. I've personally done this and it worked (and we had error correction) but for some reason the manufacturer said specifically not to. Maybe this is a serial flash only issue though. Can't say I've had that much experience with a range of flash parts.