what is your question - can you get the HD signal from a AJ-HD150 into an AJA I/O ? No. The AJ-HD150 has standard def outputs to feed the I/O, but it does not handle HD. Unless you are refering to the new I/O HD, which is not released yet.
if you are doing an HD job, obviously firewire from the AJ-HD1200A into FCP will look better, than standard def, from either the HD150 or HD1200A SDI output into the I/O. Most people who deal with HD prefer to work in HD, and then downconvert their output at the end. So even on a hi end example (HDCam 1080i job or Varicam 720p job), few are going to downconvert to SDI SD, just because the job will be delievered in SD (like on Beta). Most will edit and master the entire show in HD, and downcovert for delivery.