As you found, LabKey Study provides fine-grained access control on a dataset-by-dataset basis and we improved this for the 21.3 release. Fine-grained access control for sample types is not currently an option, unfortunately. You could of course put the sample types in different folders and grant Editor permissions to different groups of users in each; you could even use a filtered schema to make all the sample types readable in a third folder. There are likely some downsides to this approach.

FYI: We have created custom security roles and implemented advanced security options to meet the specific needs of our clients; let us know if you have any interest in discussing.

Adam