For the 4-port LAG, make sure the physical ports have no settings other than the channel-group command. You then need to set the appropriate commands on the port-channel (e.g. MTU 9216, vlan, etc). I usually make the LAG a trunk (tagged), so you can run a management VLAN on here too.  Also; if you reserved 1 port per physical switch for management, and you plug both switches into your LAN, in theory, spanning-tree should block one of the 'management' connections, but if, for whatever reason, the switches (spanning-tree) decide to block the LAG, you could run into the symptoms you are experiencing.
I am trying to complete configuration of JF on 2 Dell powerconnect 6224 connected to a EQ PS6000 (2 controllers, 4 ports each).  PC switches are connected via 4-port LAG, not stacked.  Using ESXi 4.1.  All vmk's are in the same vswitch, so I beleive the vswitch and vmnic's are set correctly.  I can ping jumbo frames (vmkping 8000) to TWO of my SAN ports / IPS, but not the other two. I have double checked the switch port settings (more like 50 times) and they are all the same.  The two SAN ports / IP's I cannot ping with JF are on physical switch 2.  Also, I can vmkping -s 9000 across all vmk's / IP's of the vswitch and ALL return satisfactorily.    The odd thing is, typically when JF are not working and you vmkping -s 9000, you get a response "sendto() failed (Message too long)." I DO NOT get this when I ping the 2 non-working ports - it just completes with 100% packet loss.  When I ping these two ports / IP's with 1400 bytes, the return as expected, so I do have connectivity.  I will not be surprised if I have missed something simple.  Any ideas appreciated.
Jumbo Frames on powerconnect 6224 and EQ PS6000 - 2 ports work, 2 do not