DDE 29

I note that in the new DDE 29, the list of cpu types that objasm 4.07 will accept includes

 --cpu=Cortex-A53
 --cpu=Cortex-A53.no_vfp
 --cpu=Cortex-A53.no_neon.no_vfp
 --cpu=Cortex-A57

Can I conclude from this that the Raspberry Pi 3B+ (Cortex-A53) can now be programmed with objasm to use vfp or neon hard floats?

Yes. However this isn’t anything new (I believe it was objasm 4.00 which introduced VFP & NEON support, and that was released several years ago).

Is that only using the inline assembler, or can the C compiler automatically use hard floats once the —cpu flag is set appropriately?

AFAIK it’s still only objasm which supports VFP/NEON. The C compiler (including the inline assembler) can’t use them.