I would guess that if you have Aruba-compatible DACs they work with TrueNAS too. Get some from fs.com etc. and see how they work. I think I've used fs.com Aruba compatible DACs with Cisco/Huawei switches and they work fine.
Not sure why any vendor should have restrictions on what to use within a rack, with other vendors we've just used "Generic DACs" from fs.com and they work fine but Aruba seems to need different cables.
Hope that changes as I've heard that Aruba has lost some bids because of the SFP/DAC compatibility or the prices. Anyways something to do with their strict policy with these.