Based on my knowledge, Exchange Online doesn't provide additional immediate scanning for items when they are imported to the mailbox from Azure.
From the PST import workflow, we can know that M365 analyzes the data in the PST files before starting the import job, but it doesn't mention that M365 will provide virus scanning in this process. Since I mainly provide support for Exchange, if needed, you can post a new question specifically only with azure-blob-storage tag to know if Azure Blob provides any virus scanning feature.
For your reference: Overview of importing your organization's PST files.
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