My question really is whether the indexers can recognize the accents.
YES , the search engines can recognize the accents of your
metatags however this will directly affect the search results in them, I would simply advise you to add the encoding that you occupy, for example:
Here you can see a search on google and compare the difference of results with this other than the word Avion and Airplane , respectively.
As you can see, the first search with the word Avion threw us:
About 100,000,000 results (0.63 seconds)
And with Airplane :
About 56,800,000 results (0.66 seconds)
Here you have another example with two more words without accents, and same with tilde; massotherapie montreal , massotherapie montréal .
In conclusion you can put them with tilde but in one way or another the search will be directly affected through browsers.