No, it does not support NAND flash at this time.
The problem is that NAND flash programming is not so much standardized as
NOR flash programming. NOR flashes are (almost) always connected to
the addr / data bus of a controller and all that needs to be know to access them is
the address (and some marginal details such as bus width).

NAND flashes can not be easily put into categories, so there is no easy "generic" solution.
What we can and will do is provide small utilities for different eval boards that
allow porgramming the NAND flash of a particular eval board.

An other thing that a customer can do is to take our SDK and write a small program himself
which does this. We could also do this and provide source code.

In Short: We will not add this to J-Flash any time soon, but there are other options
such as writing a small utility yourself or paying us to do so.

--Rolf