PaulThomas said:
No it's not. The authority of a CFI to log PIC when giving instruction is based upon, well, being a CFI giving instruction. Touching the controls or acting as PIC has nothing to do with it. (Read the regulation - this is one of the clear ones)
And, yes, you may give instruction in a tailwheel without the endorsement.
But that's just about writing numbers in a logbook and the legality of giving instruction in an airplane you're not qualified to fly. The better issue was raised by those who questioned whether you should be giving instruction in an airplane you're not qualified to fly.
Picture a mishap on a xwind landing. The FAA sends you a letter of investigation and a prelude to certificate action or a CFI retest. Your best explanation is, "Well, no, I wasn in no position to take over the airplane I was teaching in, but it was legal, wasn't it?"