Final answer:
Agentless RUM in Dynatrace is utilized when direct JavaScript injection isn't possible, which may be due to source code restrictions or content security policies. It is not used for deep code-level monitoring, server resource monitoring, or when integrating third-party monitoring tools.
Step-by-step explanation:
Agentless Real User Monitoring (RUM) would be used in a Dynatrace environment when direct JavaScript injection isn't feasible. This scenario can occur if you cannot modify the source code of a web application or if you are dealing with restrictive Content Security Policies that prevent the use of inline or external scripts. Agentless RUM is instrumental in cases where the usual JavaScript tag cannot be installed. However, it's important to note that agentless RUM does not provide deep code-level monitoring, which requires a different setup entirely. For server resource monitoring or when using third-party monitoring tools, other solutions within Dynatrace or alternative integrations would be employed.