Are the SMART DMUs FRA-compliant in the old sense (solid boxes, no crush zones) or the new sense ("equivalent" FRA compliance using crush zones)? I'm pretty sure the eBARTs are the latter. Technically, a FRA waiver is needed to use the crush zone approach, which is really what Caltrain is asking for.

In a typical grade crossing accident the crush zone should not be a factor. Perhaps, if a heavily loaded truck is hit at speed it might come into play - if the truck is a substantial fraction of the mass of the rail vehicle. But ordinarily it will not, any more than an old-style FRA-compliant structure would be damaged. FRA compliance, however it's done, is oriented mainly at train-on-train collisions.