The "Interested Vendors" list on SAM.gov can be effective for identifying potential teaming partners, but it requires careful vetting. The list is essentially a public record of businesses that have expressed interest in a sources sought notice or other solicitation.
From the buyer's perspective, the purpose of a sources sought notice is market research. It helps the contracting officer determine if there are enough capable small businesses to warrant a set-aside, for example. Companies on the "Interested Vendors" list have already demonstrated some level of interest in the requirement, which can save you time in partner identification.
However, the list does not indicate the seriousness or capability of the listed firms. Some may be serious contenders, while others might be casting a wide net or simply collecting information. You will need to conduct your own due diligence on any firm you contact from the list. Look at their past performance, their relevant experience in IT staffing and training services under NAICS code 541519, and their financial stability. A well-constructed capability statement and a clear understanding of their role in a potential team are good indicators of a serious partner.