What screening does and does not tell you
A current check confirms that a person has been assessed as suitable to work with children at a point in time. It does not describe their work, their reliability or their understanding of your site rules. Treating it as the whole of due diligence is a mistake in both directions: it is essential, and it is only the entry requirement. The rest of the comparison still has to happen on competence and supervision.
The practical risk is not usually a provider with no checks. It is a provider whose records drift out of date because staff change and nobody updates the register. Ask how many people the provider expects to attend your site over a year, including relief, and how each of those is verified before their first shift. That question exposes the gap between a policy and a working process.
