Fire mechs are too slow, there would have to be a new type made for ERTs, a reskin of the Odysseus would be cool too.
EDIT: one major problem with ERT teams is their response times. Either they take their time and arrive too late or leave vital gear behind. There are a few ways this can be improved:
•units should spawn with internals, full armor, magboots, combination sec/medi hud and insulated gloves.
•flashbangs and other items should not just be in boxes. Have a few loose.
•most larger objects that need to hauled around should spawn on the shuttle.
•you should be able to create an ERT member in the lobby. (Limit hairstyles to just the buzzcut, they are a quasi-military unit anyway)
•belts should spawn with a few items. (mainly sec belts)