[stboz]

This warning and command was broadcast of the guard channel every pilot is required to monitor for emergency air traffic control instructions...

Are other aviators in the area of concern stating they heard the "warnings?"

[WhiskeyX]

“Are other aviators in the area of concern stating they heard the “warnings?””

I haven’t seen any news reports about direct evidence, but such evidence does seem to be implied by the response of the NATO Secretary General. See:

Q (CNN): The Russians are saying the plane was shot down over Syrian territory and never went into Turkish territory. Are you convinced that it was shot down indeed over Turkish airspace and that Turkish airspace was indeed violate?

Secretary General: The Allied assessments we have got from several Allies during the day are consistent with information we have been provided with from Turkey. So the information we have from other Allies is consistent with what we have got from Turkey.

http://www.nato.int/cps/en/natohq/news_125052.htm?selectedLocale=en

[Krosan]

There was a Dutch plane nearby that confirmed hearing the warnings in guard channel.

[Article in Dutch] http://www.rtlnieuws.nl/nieuws/buitenland/piloot-zag-turkse-f-16s-russisch-toestel-tientallen-keren-gewaarschuwd