Yes you may, but you might be better served using the Unibrain five-port, rather than the Unibrain three port hub. Here's a topology using two three port hubs:

              Hub_1
HOST --- = p1 |
              | p2 = --- DEVICE         Hub_2
              | p3 = ------------  = p1 |
                                        | p2 = --- DEVICE
                                        | p3 = --- DEVICE

This works out of the box for self-powered FireWire devices. Bear in mind that any bus power devices will require an optional power supply. Also, the total device count on a single branch cannot exceed 16, and understand that aggregating multiple devices on a single port does create a potential for over-saturating bus bandwidth if several high-performance (e.g. HDDs) devices are sending data at once. However, for most uses, tiered hubs are fine. Lastly, put your slowest devices on the end of the chain.

Hope this was helpful.

We needed to test some samples of Biwin Semiconductor (HK) Company Limited's 300X CompactFlash Cards. In the interst of trying something new we decided to try change test platforms. Rather than use our iMac, we used a Xubuntu Linux desktop and our high performance Delock 91694 FireWire CF CompactFlash Reader FireWire 800/IEEE 1394B UDMA. The great news is that the FireWire reader works just fine under Linux, and we were able to complete our benchmarks tests on these non-DLSR grade CompactFlash cards.

We ran Xubuntu 12.04.2 LTS on our test machine, am Intel Core2 6300 @ 1.86GHz with 2GB RAM. The reader was our Delock 91694 FireWire CF CompactFlash Reader FireWire 800/IEEE 1394B UDMA. We used Disk Utility 3.0.2 to create the benchmarks. Here are the benchmarks for the Binwin cards.

Delock benchmarks versus our now discontinued FireWire CompactFlash Reader

Power Supply Information for FireWire Repeater Hubs Like Unibrain's Fire Repeater Line by everythinghereplus