If I'm reading your question correctly, you're saying can a widget-maker be accredited to certify other widget-makers to 14001 and 18001? Well in theory, yes. But being a certification body seems to be a significant line of business - if any SME was going to set up as a certification body alongside their "day job" I'd guess one of the H&S Consultancies would be the obvious, but I don't know of any that have done it. You'd need enough auditors and lead auditors with knowledge and experience of both the business sector and auditing to keep it going, and your own internal audit team to demonstrably maintain standards. If you're looking to certify your own widget-making operation then I suspect you'd need so many "Chinese Walls" in place to satisfy the accreditation requirements that it'd be easier to just use an external body.