You are quite right that these are not event verbs. Nor are they impersonal verbs in general; they are just one type. The most frequent term in English linguistics for these is verbs of occurrence.

Not everyone defines "verbos de acontecimiento" the same way or gives the same examples. In particular, weather verbs are not always included in this class.

"verbos de acontecimiento (ocurrir, sobrevenir, suceder, acontecer, presentarse)"
http://books.google.es/books?id=aew18_Fkfi4C&pg=PA112&lpg=PA...

"los verbos de acontecimiento como suceder, ocurrir, y los verbos meteorológicos [...]"
http://www3.unileon.es/dp/dfh/SEL/actas/Rodriguez.pdf

This is from a thesis on pseudo-impersonal event verbs:

"EXISTE EN ESPAÑOL UN GRUPO DE VERBOS FORMADO POR ACAECER, ACONTECER, OCURRIR, PASAR, SOBREVENIR Y SUCEDER QUE SE ESPECIALIZAN EN PRESENTAR O INTRODUCIR EVENTOS. ESTOS VERBOS SE ADSCRIBEN A LA ESFERA DE LA EXISTENCIA Y SIGNIFICAN, DE MANERA GENERAL, ‘PRODUCIRSE UN HECHO ESPONTÁNEO’. SE CONOCEN COMO VERBOS DE “ACONTECIMIENTO”."
(Sorry this is all in capitals, it's like that in the source)
http://siep.posgrado.unam.mx/tesigrado/consulta/detpaterno.c...

"verbs of occurrence: appear, disappear, go, come, arrive, depart, vanish, fade, happen:"
Angela Downing, Philip Locke, English Grammar: A University Course, p. 85
http://books.google.es/books?id=8ii6JXP6BO0C&pg=PA85&lpg=PA8...

"(d) verbs of occurrence (succeed, happen); (e) weather verbs (rain, snow)."
Routledge Dictionary of Language and Linguistics, p. 1253
http://books.google.es/books?id=rhvDiOxOUe4C&pg=PA1253&lpg=P...

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Note added at 29 mins (2012-11-27 19:23:11 GMT)
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"48.3 Verbs of Occurrence
Class Members: ensue, eventuate, happen, occur, recur, transpire"
Beth Levin, English Verb Classes and Alternations: A Preliminary Investigation, p. 260
http://books.google.es/books?id=6wIZWOrcBf8C&pg=PA260&lpg=PA...

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Note added at 3 hrs (2012-11-27 22:22:12 GMT)
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In terms of raw numbers of Google results, "verbs of happening" (90) and "verbs of occurrence" (82) are almost equally common. It is difficult to quantify the variants "occurrence verbs", "happen verbs" and "happening verbs", since so many results for these combinations are simply irrelevant conjunctions of the two words.

But I think that if you review the results you can see that "happening verbs" is somewhat more common in TEFL (teaching of English as a foreign language) and in non-native writing, and "occurrence verbs" is more common in texts, particularly books, written by English-speaking linguisticians, such as those I have cited, though there are clearly exceptions.

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Note added at 3 hrs (2012-11-27 22:24:43 GMT)
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Sorry; in the last paragraph above I meant "verbs of happening" and "verbs of occurrence". "Verbs of happening" is a less formal term, the kind of term one would use in practical English teaching rather than academic grammar.