You could configure the no-import-side-effect rule to ignore the side-effect import of the rxjs-imports.ts module, using configuration like this:

"no-import-side-effect": {
  "options": {
    "ignore-module": "rxjs\\.imports$"
  },
  "severity": "error"
}

However, that won’t ignore the side-effect imports within that module. To ignore those, you could use a TSLint comment flag at the top of the file:

/*tslint:disable:no-import-side-effect*/

You’d need similar comment flags in polyfills.ts and test.ts, too.

If you were to rely solely on that approach, you would not know about unused RxJS side-effect imports. rxjs-tslint-rules performs static analysis and can be configured to fail if there are unused RxJS imports — that’s the biggest advantage of using the rule extensions.