I have taken a screenshot from my own copy of SADX in 1920x1080 to show the similarities to Refragg's run's HUD
The HUD of the game is noticeably affected in the same way as in Refragg's run, he just has the game resolution upscaled, as for the blinking health bar, this likely happens for the exact reason DrMinus mentioned. Though I can't prove that one way or another as I obviously do not run the same setup as Refragg.
As for Niczur, he's just clearly running SADX's PC disc version on the default resolution of 640x480, and nothing is strange about his run in the slightest. There are hundreds of ILs and single segment runs of SADX on the PC disc version on youtube, twitch, and speedrun.com you can compare it to and it's pretty clearly that version.
As for why neither of them have replied to this thread, it's honestly pretty simple. TSC's forums are not a relevant portion of the sonic speedrunning community and have not been such for many years, while the TSC stat pages themselves maintain some niche use from modern runners, these forums are easily ignorable and Refragg and Niczur could be wholly unaware of this thread ever existing.
On top of that, Refragg and Niczur have been well-trusted runners and even moderators of the SADX community on speedrun.com and discord for multiple years now. They have also been top level runners for over half a decade. They've been in position to be caught and scrutinized as cheaters for this whole time, and nothing has come to light about these runners playing their runs on emulator. These exact runs have even been submitted to speedrun.com, and clearly would've been caught by their moderators, who are highly knowledgeable in the game themselves and would be a good authority on whether or not someone is cheating, and neither were rejected when they were submitted.