XigmaNAS

Is it ok to use port multiplier for nas4free?

This is hardware, not software. Read this and try to apply article to sata multiplier

my question about hardware

In general:
Usually hardware have driver chips, with his bandwidth. If your controller have SATA3 connector, then chip driver cannot work faster then 6Gb/s
In case multiplier you will have summary bandwidth less then 6Gb/s because controller must calculate address and switch signals.
If you plan connect 4 drivers to one port - you will have ~ 700 Mb/s per drive. This value lowest *2 then old PATA speed.

For a more direct answer, possibly.

First, does your SATA port you are multiplying support it? This is often "No" here, or sometimes a "kinda but not really" that can be worse.

Next, does FreeBSD recognize it? Again, this is hard to find out.

You are generally better off just buying some more SATA ports.

Port Multiplier works well for me.
I use the N54L with the modified BIOS and a Fantec QB-35US2 (4xHDD housing) via eSATA port.