This app was mentioned in 2 comments, with an average of 1.00 upvote
Does windows have better support for this? Unless you're going to use remote desktop or something, but that will be so slow.
Does your motherboard support IPMI? there's an android IPMI client (I haven't tried it)
You could also use a usb-to-serial converter + this app or similar. (if your mobo has a serial output, which seems likely) (again I haven't tried this either). FreeNAS doesn't turn on the serial port by default, but you can turn it on in the settings.
I'm kind of curious if either of these will work.
Cool. It does exist! Googled "android ipmi":
https://play.google.com/store/apps/details?id=com.smc.smcipmitool&hl=en