As far as I know - No.
You cannot transfer a call to the 3cx fax server as t38 is different and is done on the invite. i.e. The call comes in as an invite and 3cx looks up the inbound rules. If that inbound rule says send it to the fax server then 3cx sends a notification to come back using t38, then when that comes back it routes it to the fax server.
I think your question was whether it has an "auto fax detect" and the answer is also no.
To be honest though with VOIP DID's being so cheap why not get an extra line? My customer just added 25 DIDs to their account with Broadvox so each of their Real Estate Agents has their own personal fax line now. $1 per DID per month.