These AT&T facilities were hardened against EMP to the era's military design standards, and AT&T participated in validation experiments using both actual nuclear detonations and EMP simulators. I've never seen any indication that AT&T thought the electromechanical switches had an advantage in this context, but it's an interesting question if they performed any evaluation. In general, though, EMP protection was done at the "envelope" of the facility, and equipment inside of the facility did not need to itself be EMP hardened. Hardening of the facility was achieved mostly by a shielding system embedded in the outside walls, and of course AT&T had already performed considerable research into suppressing transients on the outside plant due to lightning.
Crossbar switches were indeed in use in the AUTOVON network for simple scheduling reasons, a number of AUTOVON switches were installed before the 1ESS was ready. Eventually all of the 5XBs were replaced by 1ESS. Some Automatic Electric switches were used at AUTOVON sites outside of Bell territory, these were at least semi-custom (AE just called them "the AUTOVON switch") electromechanical machines.