AFAIK Yes, FreePBX FAX Pro module can.
You’ll be able to set up (virtual) FAX Extensions (one or more, depending on you requirements), create (one or more) Incoming Route to route any incoming call (FAXes) to those specific DID numbers to (virtual) FAX Extensions and - if you want - let FreePBX to send received FAXes as PDF or TIFF to each virtual FAX Extensions’ pre-defined e-Mail account.
Concurrency of incoming calls is a matter of your ISDN PRI Line.
The T.38 plays a role when you want to implement FAX over IP (FoIP), but, from what you wrote, your scenario - valid for Voice calls and FAX calls - is implemented around ISDN Line (correct me if I misunderstood):
ISDN PRI Line (with “n” active bi-directional digital channels) -> external ISDN PRI/SIP Media Converter (or internal ISDN PRI PCI Card) -> FreePBX Distro (through DAHDI) system.
In the scenario above you don’t need any ATA to G.3 FAX until you need to have one or more G.3 FAX machine to send FAXes from (you can ask users to use the actual ARI User Panel to send them “digitally”, no paper waste involved) or to receive forwarded FAXes yet received by the FreePBX Distro system.
No T.38 is needed until you want to switch to use SIP Trunking to your SIP Provider (mandatory requirement: it should support T.38).
If you have dedicated DIDs to use for receiving FAXes you can avoid to use DAHDI’s FAX recognition tone (incoming call from one of that DID number will always be considered and managed as an incoming FAX call), which improve incoming FAX management (the system shouldn’t recognize anything).
Virtual FAX Extensions could then manage FAXes (received and to send them, when required) through User Portal.
I’ll wait and test FreePBX Distro 6.12.65 to see how new UCP is. FreePBX FAX Pro module is (and will be) agnostic and so it will work on actual FreePBX Distro 5.211.65 (with ARI User Portal) or the new FreePBX Distro 6.12.65 (with UCP User Portal) even if, once coped with this latter one, you could expect development and new features being introduced (new features are frozen in FreePBX Distro 5.211.65) as requested/needed.