An "entry clearance vignette" is a visa, so you should have no problems. To be completely sure, though, you might want to check with the airline in advance -- they're the ones tasked with actually enforcing the requirement.
Some of them say "entry clearance" in the heading field instead of "visa", but they are visas all the same, in contexts that are not bound by the UK government's terminological ideosyncracies. Here is a PDF from gov.uk showing examples of both kinds of vignette. Notice that both of them are coded as visas in the machine-readable field (first character of line 1 is
Article 3 of the Schengen Visa Code defines exemptions from the airport transit visa requirement thus:
- The following categories of persons shall be exempt from the requirement to hold an airport transit visa provided for in paragraphs 1 and 2:
(a) holders of a valid uniform visa, national long-stay visa or residence permit issued by a Member State;
(c) third-country nationals holding a valid visa for a Member State which does not take part in the adoption of this Regulation, for a Member State which does not yet apply the provisions of the Schengen acquis in full, or for Canada, Japan or the United States of America, when travelling to the issuing country or to any other third country, or when, having used the visa, returning from the issuing country;
In item (a) the visa is supposed to be in the "uniform format" (which describes UK visas of first kind), but this requirement is not present in item (c). So a non-uniform-format visa from the UK is sufficient to exempt you from the ATV requirement.