The tiles did not have a 'to' but did have a 'for', and as the dative case can be translated as 'to' or 'for', I translated the sentence as The orator sends a letter for me. Whilst this is not as usual a translation as The orator send me a letter or The orator sends a letter to me, I think it should also be accepted as grammatically correct.
Or does the use of 'ad' mean only 'to', whether explicit or implicit, is correct?
The use of the preposition "ad" is very explicit as direction towards. It takes an accusative object and so there is no real indirect object in this sentence. If it was "mihi" instead of "ad me", you could make the argument for the translation "for me", but from context, a regular indirect object would still make more sense here.
literra means "letter" as in like letter of the alphabet. so in plural it can mean "letter" like a letter you would send to someone. In that case I think the word "epistula, epistulae - letter" (like the latter definition) would be less ambiguous, but the plural use of "littera" still is used in Latin . Notice that "litteras" can also mean literature in general
Except right now it doesn't accept "literature" (and yes, I did report it.)