SMLT is a form of aggregation or MLT that lets you distribute an aggregated trunk over several switches instead of using spanning tree. Failover times is usually measured in ms as in 100ms up to 500ms instead of seconds like it is with spanning tree. In many cases you really don't notice anything at all from a client-server perspective. Although at the current time I dont know if any other companies implement it other than Nortel / Avaya, but it that case it probably has a proprietary setup/name. Havent been able to get any hands on with Cisco Nexus yet to see if they allow link aggeragation over their "virutal switches" that can be setup to cross chassis. And as I said, I dont know if Alcatel Lucent has something similar.http://en.wikipedia.org/wiki/Split_multi-link_trunking
As for the Spanning Tree topology changes. The switch should be able to log them and output them as syslog/snmp-trap. At least Cisco logs it so it's easily viewed by your choice of log server. And since most solutions can easily be setup to give you a mail/sms or parse it to whatever you need depending on the event. But that only gives you a heads up when the topology changed. if you on the other hand need to know the exact time of a the topology change in a lab-setup, it might not be for much use. Have you looked at the debug features of each switch instead of trying to use wireshark ?
A more specific solution is hard too really help you with. Would probably be best to ask somebody that have more experience with Alcatel Lucent if the generic ones like spanning tree doesnt work. And it may be that the solutions isnt neccessarily completely limited to the network but need to be a hybrid of network/server, or could even be one of education of the users if its not a technical must have that you recover within 2 seconds. Even though your description of the network is simple enough, it really doesnt say anything about the function of the application. You mentioned that you use multicast. Are sources distributed to multiple switches or single source connected to different switches, etc. Do you need the full mesh because of bandwidth usage, etc?
While I probably cant do anything about it, I'm a stickler for trying to state things cleary. A quick search mentions Ring RSTP support in some Alcatel-Lucent switches that is supposed to provide sub 100ms convergence time, but that would require you do change your full mesh to a ring topology instead, etc.
From earlier discussions I would say that we arent really more than a handful of people here in the TR forums that deal with larger enterprise networks though, so some posts in other foras might be a good thing or perhaps a mail to your Alcatel Lucent supplier for ideas.