Thanks to both @CGGXANNX and @lurker888 for confirming that it will work when HW offloading is active (at least on the RB760iGS and RB750Gr3). I was reasonably sure this used to work, but I had been trying some things out in the lab after this post by @lurker888, one of them being to have the pvid of the bridge use the same vlan as a vlan interface on the bridge (a deliberate "misconfiguration" that will work as long as the bridge interface has frame-types=admit-only-vlan-tagged). But after I finished that experiment and set the bridge pvid back to 1, I didn't set frame-types=admit-all again. So I wasn't seeing traffic from the untagged hosts. After resetting to receive all frame types, I am able to see the other hosts. Thanks!
I was just surprised when I tried viewing the bridge host table and it only had internal addresses listed. (related to my post about determining the port a host is connected through). And just learned another new thing today from @CGGXANNX post in that thread.