In linguistics you can't really talk about "silent letters". Orthography and phonetics follow separate evolutionary paths in most languages, and orthographic spellings rarely have one-to-one correspondences with phonetic sounds.
tl;dr: The closest term that comes to mind would be "articulated".
Usually in phonology if you're talking about sounds not being produced, there's some phonological process involved in not producing them, and so the term used to describe them is usually a variation of the name of the process that causes them not to be articulated. E.g. in "vehicle" the /h/ is the result of elision, so you could refer to the absence of this phone as "elided-h". More specifically, the elision is caused by lenition or weakening of the sound, so "lenited-h" would be a little more precise.
In some cases, a sound not represented in the orthographic form of a word can be heard when spoken aloud (e.g. the /p/ that is often heard in the pronunciation of "something"). In these cases—as with elision/lenition—the "articulated" sound is often referred to by the name of the process that causes it to occur. In the case of "something", the /p/ is the result of excrescence (a type of epenthesis) and so would be called exrescent-p or epenthetic-p. But there aren't really terms for talking about why sounds are not omitted.
One other potentially relevant term here: when two different pronunciations are acceptable in the same speech community, as in your 'vehicle' example, it's called free variation. But this is not just restricted to pairs where a particular sound is omitted or articulated in some varieties but not others. /tə'meto/~/tə'mato/ is another example of free variation in which the difference between the two varieties is in the quality of one of the vowel sounds.