Quite often they have a coffee maker, which you can use for tea. You need to check the room description on their website (and take your own teabags).

I can only answer for Las Vegas.

Most of the casino hotels do not have coffee and tea making facilities.

The exceptions I can think of are
Bally's North tower (Only some rooms)
Orleans
Gold Coast

Some of the suites have facilities too, but I'm too cheap to pay for a suite, so I can't help there.

We buy a $10 Hot Pot (they don't do kettles) from Walgreen's.

All the hotels we have stayed at other than in vegas had hot drink making stuff in the rooms

Might be best to name the hotel for a more specific answer.

If tea is your choice I would take a travel kettle. The water temperature on the inroom coffee makers never reaches the correct temperature and you also often find a coffee taste still lingering.