should I report the emissions from my vehicle fleet in the questionnaire

Own fleet almost always falls under scope 1

Yes, you include the emissions from your company vehicles — and in most cases they fall under scope 1, not scope 2 or 3. Scope 1 is the direct emissions from sources that the enterprise itself owns or operates, and a leased vehicle or own van registered in the name of the business falls precisely under that. This applies to the fuel burned in your own vehicles, so diesel, petrol and gas. Electric company vehicles are a point of attention: the electricity they charge falls under scope 2, not scope 1 — check that distinction if your fleet is partly electric.

Edge cases are employees' private vehicles used for business mileage and vehicles from subcontractors or transport providers you hire. These usually fall under scope 3, category business travel or transport, and are therefore not required in a basic module answer if you do not keep figures on them. It is worthwhile to make that distinction explicit in your comment on the questionnaire, so that the customer does not assume your entire chain is included when you have only specified your own fleet. If you do not yet have figures on scope 3, it is more accurate to leave that field empty or to state that it is not yet measured, than to present an estimate as a hard figure.

Substantiation: scope classification from the GHG Protocol

This classification comes from the GHG Protocol, the source behind the scope 1/2/3 classification that the EFRAG VSME basic module also applies for the reporting of greenhouse gas emissions. For the precise delimitation of what falls under scope 1, see what is meant by direct greenhouse gas emissions; for the purchased electricity of electric vehicles see what is meant by indirect emissions from purchased energy. Whoever struggles with how scope 1, 2 and 3 fit together in one answer will find a more compact overview at how to correctly complete the question on scope 1, 2 and 3 emissions.