Instructional vocabularies routinely include plural forms, and it is simpler to list those using the definite article. Going from le / la to les is smoother than going from un / une to des. The latter requires knowledge of the usage of de, and to a novice that would be a leap.

I highly doubt that using “le/la” is a common practice, and am sure that is it not a good practice, only by the fact that a lot of names begin with a vowel (or a silent h), and thus have the same article for masculine and feminine.

As a few examples, guess if these names are masculine or feminine…

L’armoire, l’histoire, l’entonnoir, etc.

Un/une is better because the elision is not done with une :

Une armoire, une histoire, un entonnoir, etc.

I wonder how the Oxford take off in French book deals with these names.

Anyway, “serious” dictionaries do not use a repetition of the name with an article, but use a specific notation instead, for example [n.f] for feminine nouns and [n.m] for masculine nouns.