Implement a Python function that validates and converts a date string into a standardized RFC 3339 format, ensuring compliance with UTC timezone.

- **Input**: A string representing a date in a recognizable format.
- **Output**: A string representing the date in RFC 3339 format (e.g., "YYYY-MM-DDTHH:MM:SSZ").
- **Special Rules**:
  - Parse the input string into a datetime object using `dateutil.parser`.
  - If the datetime object includes timezone information, convert it to UTC.
  - If no timezone information is present, assume the input is in local time and localize it to UTC.
  - Format the datetime object into an RFC 3339-compliant string, ensuring the suffix is "Z" for UTC.
  - Raise a `ValueError` if the input string cannot be parsed or does not adhere to the expected format.