There were two Lt's on my course when it was run at Bullford..so it was not recent.
One was a UOTC on two year posting (Remember him being a Cav type!)
other was RE TA, but i am sure he was about to be posted to TAOC as a DS....
There are officers in the APTC -ie Late Entry officers who joined the APTC as NCOs.
There are no jobs for Direct Entry officers as PTIs; PTI tasks are conducted by APTC SNCOs and qualified JNCOs in most units.
There are some qualifications that officers can gain (ETL has already been spoken about) and there is a unit fitness officer (IIRC) - usually the Bn or Regt 2IC in major units, responsible to the CO for the fitness of the unit. There are courses that are designed to assist in planning fitness training but the majority of fitness instruction in the Army is done by NCOs.
The Royal Marines have a qualification for DE officers as PT officers.
All I can say it that on a RMAS fam visit, we asked the PTI whether officers can be PTI's. He said No, and that only two officers have been PTI's (or vice versa). And they were commissioned from the PTI corps when they were WO2's or WO1's- forget which rank may even have been SSgts.