I can't see the humans not getting in on the bonding stuff really. In terms of integrating humans into the empire, it would be a useful tool, a common cultural point that could be spread easily. Throat surgery isn't required to speak Tau, several Inquisitors have demonstrated fluency in it in other fiction, though it's possible that particular human had it done to rid him or herself of the accent.
As for the other two things, they are certainly interesting as well.
In theory, the Tau would have had more than enough time to study the human brain to allow for human piloted battlesuits. It is important to note that they are piloted by neuro-synaptic links (presumably with manual backups). So from that perspective, either the Tau have developed the appropriate neuro-link or the humans simply pilot their suits manually. The scruples to be had there have more to do with the idea that the Tau would trust humans with that level of tech. Many, albeit Imperial, perspectives have humans as footsoldiers, but always seem to imply that the Tau don't trust the humans. I always found this a bit ridiculous, given the number of centuries that humans have been born within the Ethereals' territory. It's been more than enough years for there to be dedicated human military elements in Fire Caste coalitions.
As for the Devilfish, it is rated to work in a vacuum and it can deploy from high altitude anyway, so I would imagine it's a relatively easy mistake to make.
