Ha, I think a lot of LR fans have had the same thought.
More than one comedian, not to mention MAD Magazine, has gotten mileage out of reconsidering the LR/Tonto relationship in a more realistic light.
Does "What you mean 'we', Kemo Sabe?" ring a bell? 😉
I admit I've never seen a serious, reliable account of how individual Indians mingled, and were treated, by white townsfolk in the period where the series is set.
But even thoughtful, humane icons like Mark Twain had a strongly prejudiced-- i.e. low-- opinion of Indians.
To be fair, the series did show poor Tonto putting up with a lot of demeaning, racist crap from both outlaws and solid citizens. And the series deserves credit for "preaching" the virtues of tolerance, civility, respect, and fair play for all law-abiding people.
But, all things being equal, it seems extremely unlikely that Tonto would be well-received, or even respected, when he's running errands or following orders on the Lone Ranger's behalf. Exactly as you say, he'd be treated with suspicion, contempt, and derision, or worse.
And, sad to say, he definitely wouldn't have been allowed to stay in a "decent" hotel in that era, with or without the Lone Ranger-- unless, maybe, the LR insisted that Tonto is his "manservant", and Tonto ditched his usual garb and wore suitable white man's clothes for the occasion.