It's definitely possible to create 2GP dependent packages where the Parent Package is Health Cloud, FLS, or any other Managed/Unlocked package app.
You will need the Health Cloud Package to be installed in scratch org for this and you need below in your project sfdx-project.json
file. Here "04t..." will be the latest Health cloud package ID.
Check the dependencies section docs for more info
"dependencies": [
{
"subscriberPackageVersionId": "04t..."
}
],
Also additionally you will need to make sure you have the necessary feature and settings enabled in your project-scratch-def.json
file
For example, for Health Cloud you will need the below features
"features": ["ContactsToMultipleAccounts", "HealthCloudUser"]"HealthCloudAddOn"]
Watch this session to see how dependent packages work.
Also, I wrote a blogpostblog post on how to approach it here