"This hotel does not serve lunch."
Translation:Este hotel no sirve almuerzo.
Honestly, no it shouldn't be. This is an oversight by Duolingo.
As with anything (and many responses I have given on this site), it may very well be a matter of "patois", but in almost every conversation I have here in Chile, the definite article is used.
In any case, Duolingo should take greater care with issues like this. I have seen them using "el almuerzo" in previous statements that wouldn't necessarily fit in English, and this only tears spanish learners in two directions.