You can't use native-vlan-id under the "unit XXX" stanza. And there're no untagged frames coming to us from the client's side.
Also, I can't use classical scheme cause there're other units with single-tagged frames that cross my network "as is".
I've got an answer at the other forum about this problem:
"VLANs configured with extended-vlan-bridge interfaces are forwarded
using a different daemon than VLANs forwarded using the
classic ethernet-switching daemon.
It's quite likely that you cannot share VLAN IDs between the two methods of forwarding."
Looks like this problem has no solution for now except keeping VLANs separately or making VLAN-mapping 