Hello,
The 6533 and 6534 products have an internal timebase of 20 MHz. The frequencies that this board can generate are 20 MHz/n where n is an integer. So, you can hit 20 MHz, 10 MHz, 6.67 MHz, 5 MHz, etc. If you want 1 Hz resolution at this range of frequency, you may want to take a look at the PXI-5404. You can generate clock frequencies up to 100 MHz with 1 microHz resolution.
http://sine.ni.com/nips/cds/view/p/lang/en/nid/12024
You can then export the clock from the 5404 to the PClk of the 653x board.
I hope that helps,
Allen