1. Deployment Methodology: Azure Resource Manager (ARM) is a cloud management service provided by Microsoft Azure that allows users to provision, deploy, and manage resources in a declarative manner. It enables infrastructure as code and provides a centralized way of managing resources. On the other hand, HashiCorp Sentinel is a policy-as-code framework that evaluates and enforces policies across different cloud platforms and infrastructures. It focuses on defining and enforcing specific constraints or rules on resource deployments.

2. Scope of Application: Azure Resource Manager (ARM) is designed specifically for managing Azure resources and services. It is tightly integrated with Azure and provides capabilities for provisioning and managing resources within the Azure ecosystem. On the other hand, HashiCorp Sentinel is a more agnostic tool that can be used to enforce policies across multiple cloud providers, including Azure, AWS, and Google Cloud. It provides a consistent way of defining and enforcing policies across heterogeneous environments.

3. Policy Enforcement: Azure Resource Manager (ARM) primarily focuses on resource provisioning and management, rather than policy enforcement. While it does provide some level of policy enforcement through its Role-Based Access Control (RBAC) mechanisms, it is not as feature-rich as HashiCorp Sentinel. HashiCorp Sentinel, on the other hand, is specifically designed for policy enforcement and can define and enforce fine-grained policies for resource deployments. It enables organizations to define their own custom policies and ensures compliance with security, governance, and operational standards.

4. Integration with CI/CD Pipelines: Azure Resource Manager (ARM) is closely integrated with Azure DevOps and provides seamless integration with CI/CD pipelines. It enables developers to define their infrastructure as code and include it as part of their CI/CD workflows. HashiCorp Sentinel, on the other hand, is not specifically designed for CI/CD integration. It can be used alongside CI/CD pipelines, but the integration may require additional configuration and setup.

5. Community Support and Ecosystem: Azure Resource Manager (ARM) has a large and active user community due to its close integration with Azure. It has a broad ecosystem of tools and resources that support infrastructure as code and ARM template development. HashiCorp Sentinel, on the other hand, has a smaller but dedicated community. It is part of the broader HashiCorp ecosystem, which includes other tools like Terraform and Vault. Users of HashiCorp Sentinel can benefit from the community support and resources available within this ecosystem.

6. Cost and Pricing Model: Azure Resource Manager (ARM) is provided as a service by Microsoft Azure and is included in the pricing structure of Azure services. There is no separate cost for using ARM. On the other hand, HashiCorp Sentinel is part of the HashiCorp Cloud Platform's pricing model. Users of HashiCorp Sentinel need to consider the pricing and licensing implications when using this tool.

In Summary, Azure Resource Manager (ARM) focuses on resource provisioning and management within the Azure ecosystem, while HashiCorp Sentinel specializes in policy enforcement across multiple cloud platforms. ARM is tightly integrated with Azure and provides native support for Azure resources, while Sentinel is an agnostic tool that ensures compliance and policy enforcement in heterogeneous environments.