According to
this, only
ATSServer
requires Rosetta.
correct
Intel Tiger was completely native, and did not suffer any performance limitations/issues (anyone who has run Tiger on intel knows just how impressively quick it is!)
as you say the only thing that relied on Rosetta was ATSServer, a font Server
it was just a minor part, critical to loading the window server, but nothing performance critical
thus it was used a form DRM from 10.4.1-10.4.3 (as Rosetta required the TPM key to load, without the TPM key, no Rosetta, so ATSServer would not load thus no GUI)
here is my 10.4.3 Virtual machine, and I have sorted activity monitor by Architecture and as you can see only ATSServer is PowerPC as expected
afterwards apple moved to encrypted binaries, that would only load once decrypted by DSMOS.kext and a special worded key in SMC
and by 10.4.11 everything was intel even ATSServer
most binaries in Tiger are compiled for at least SSE3, hence why it was so crucial for the hackintosh people to make an SSE3 emulator
Rosetta had nothing to do it, it was just another of many binaries that used SSE3