Hi,
you do need to configure edge ports if you do not use STP on the EXOS switches.
Promiscuous mode and VMAC are probably irrelevant to physical switches, that would be of concern when using virtual appliances connected to vSwitches, I think.
I have used UCARP as HA solution for two GNU/Linux servers a couple of years ago, I just needed to provide a layer two connection between the two servers. UCARP works similarly to VRRP or HSRP, thus if you expect VRRP to work fine, UCARP should work as well.
I do not know the Kemp LoadMaster appliances, though.
Erik