Can Thai companies with minority American shareholders buy land in Thailand?

51% Thai ownership preferred shares, 49% common shares American ownership

Service business with employees that pays VAT, social security, wage withholding etc - all done correctly for an active business.

The short answer is yes. The long answer is, as you stated, it must be an active business, filing audits, social fund payments on employees, paying taxes etc. It is generally accepted that the business will purchase the land for business use.