The supplier is not a subcontractor - they supply exactly what is requested, whether it is fit for purpose (and won't end up killing warehouse workers) rests entirely on the prime, the ultimate design authority.
The supplier can offer help in selecting and fitting, but it will be guidance,a nd guidance based on reduced information.
Sub-contracting involves a legal arrangement where authority/responsibility is devolved - the OP has said they'd consider employing an engineer from the supplier, which is a good thing.