Cisco – which 10Gb switch has native CX4 copper ports

No, they're not the same. The "uplink port" on a switch is where it connects "up" towards the rest of the network. There is generally only one (though some models have two for redundancy purposes). The uplink bandwidth is shared by all the devices trying to communicate with the rest of the network at the same time. By putting a 10Gb uplink on a 1Gb switch, it would let (for example) 10 devices on the switch communicate at 1Gb each at the same time with the rest of the network. Otherwise if the uplink was only 1Gb, those 10 devices would only be able to get about 100Mb each.

It's probably physically possible to connect your 10Gb HBA to the 1GB "Layer 3 switch" (back in my day, we called this a router!), depending on the make and model and physical connections (fiber or copper?) but your HBA would then be communicating at 1Gb.

There's no such thing as a "10gb Ethernet interface". There are a variety of interfaces and cables, suited to a variety of speeds.

• 10g base-t is the the old RJ45/Cat6 interface that most people associate with networking
• SFP+ is what we use at my site - this can be fibre or copper (direct attached) depending on needs. We use copper inside racks and fibre to link to other switch rooms.
• 10GBASE-CX4 is physically very similar to infiband and I think for a while was the most viable way of delivering 10Gb connections inside a cabinet, but I'm not sure I'd choose it for a new setup these days.

Now as to your question - you seem to be implying you're buying a switch with one type of connection to connect to devices using a different type of connection. This is obviously not going to end well.

You need to speak to Dell (and possibly other suppliers) about something that will support the CX4 connections on your storage server, plus whatever type of connection you propose to use for the rest of the LAN. (It may also turn out cheaper to replace the HBA rather than mix and match). The Dell switch you're currently looking at does not have connections for the CX4 HBA. You can't just put one type of connector at one end of a cable and a different connector on the other end in this kind of situation, there's a bit more going on here than just the type of plug.