To anyone who finds this and has a similar problem, I found a solution. While I cant seem to put hubl in the widget_attribute I can turn the whole thing into a token and place that inside the widget_block, like this;
{% set email_attribute = '{% widget_attribute "notifications_override_email_addresses" is_json=True %}["'~ row.email ~'"]{% end_widget_attribute %}' %}
{% widget_block form row.hs_id, form_follow_ups_follow_up_type='', response_redirect_id=module.form_field.redirect_id, form_to_use='{{ module.form_field.form_id }}', title='{{ row.name }}', notifications_are_overridden=True, response_message='{{ module.form_field.message }}', response_response_type='{{ module.form_field.response_type }}', response_redirect_url='{{module.form_field.redirect_url}}', overrideable=True, label='Form', response={message='{ module.form_field.message }}', redirect_url='{{module.form_field.redirect_url}}'} %}
{{ email_attribute }}
{% end_widget_block %}