Jaloux and envieux indeed mean "jealous/envious persons" but are used as substantives here so there is no suppressed noun.

Many descriptive adjectives can be nominalized and have been granted the status of nouns:

Tu es entouré de blondes.

Tu arrives dans la cour des grands.

same for ambitieux, avare, timide, méchant, gentil…

Some, like jaloux and envieux, are not officially nouns but can nevertheless be nominalized, like for example sales, lâches and sauvages.

Q.2 : Implicit noun ?

In your particular case (jaloux, envieux) : yes! There is some implicit noun.
Because jaloux and envieux are adjectives being nominalized. As such, they do carry some noun (the referent) implicitly.

Do not generalize to other adjectives such as some suggested in another answer :

• blond IS an adjective but also a noun per se. This is indeed (in the examples given) not the adjective being nominalized.
  Because of the leading article, the noun is being used. => no implicit noun.
• The same with avare, timide

You can find the categories of the words in Dictionnaire de l’Académie.

e.g. ENVIEUX, -EUSE adj. / BLOND, BLONDE adj. et n.