Are you having difficulty getting labs, diagnostics, home health, physical therapy, and other ancillary services ordered? Do these other parties claim that the problem is that you have opted out? Do they decline to perform your orders based upon your status? Is this allowed?
No, this refusal to perform orders is inappropriate. CMS provides two resources (Document #1 and Document #2) both make this clear and should answer any questions vendors might have.
This website allows you to search for a provider by name to see if she/he is known to CMS and this website allows you to search a national opt out listing.