The FAS255x onboard ports support either NetApp or Cisco branded DAC/TwinAx cables, or NetApp's X6589 10Gb Optics..
However.. what you propose is not supported, and generally will not work, except for a single controller system, or if you are only using it with iSCSI - with HA, to use ethernet, you must have a switch.
The reason is that when the system fails over, the IP will move to the other controller.. meaning you'd need a second interface on your server with the same IP address space, and Windows/Linux is unlikely to like that. There may be ways to get it work.. but it would be flaky.
> So if we get the NetApp or Cisco branded DAC/TwinAx cables connected, it will work right?
At an ethernet level, yes it will work. In terms of functionality, if all you are doing is NDMP, and it's a single controller, and you have a seperate IP range setup for just that link, it will very likely work, but it is not a tested or supported configuration, so may require some trial and error.
We only provide blessing of specific switches as part of our Cisco "Flexpod" solution, which this would not be, so I can't say this switch is specifically supported, however it does meet all the requirements for connecting the NetApp system - SFP+ ports that will take a Cisco TwinAx cable. For general utility, I might look at the 8x10GBaseT + 8xSFP+ model instead, but functionality would be the same.
For the Dell side of things, the shorter (<7M) cisco twinax cables are passive - some cards will only support "active" cables and some only support "passive", while some support both - The Intel X520 cards are an example of one that does both, but there are others.
If budget is an issue, in your position, I would try the direct attach method - it should work - but it needs to be on the understanding that a switch may be needed later.