The rules say OA don't apply to teleporting.
I'd say not - you aren't "entering their reach" so much as "appearing out of nowhere, within their reach". Unless they can both sense creatures on the ethereal plane and attack creatures on the ethereal plane, then they don't get an Opp Attack because that's where the movement actually occurs.
The key word is move. Teleporting is not moving, you simply disappear and re-appear.
Despite my initial answer, I think this probably best represents RAW. Despite the fact that the context of the statement ("You also don't provoke an opportunity attack when you teleport...") discusses only OAs provoked by leaving a creature's reach, the statement is unqualified and I can pretty much see the tweet now: "If teleportation not provoking OAs applied to only some OAs, it would say so."
PHB said:You also don't provoke an opportunity attack when you teleport or when someone or something moves you without using your movement, action, or reaction.
So if there was a glyph that triggered "when a creature enters the room", would the glyph go off if a creature Blink'd into the room?
Technically, no it wouldn't. If the trigger for the glyph was set by a player who didn't know "enters the area" had a specific game mechanic meaning, I'd probably give them some leeway. But maybe not.
Where is 'enters the room' defined as game terminology?