In their website Section 3.B. it is mentioned:
for those who have at least 1 year Australian work experience, and / or at least 3 years Overseas work experience in their nominated occupation or a closely-related occupation, then an additional assessing service is available to provide an opinion on the skilled employment claims. High-level evidence will be required to support any claim of work experience as well as completion of this form.
Their PDF for Overseas Qualification Assessment:
6. I have limited engineering experience. Can I still apply for an assessment of my qualifications?
Yes, you can still apply. Twelve months of engineering experience is a guideline only. It is possible that you can demonstrate the three competencies by referring to your undergraduate professional engineering qualifications and the project/work experience elements of your academic study. Applicants may however find writing the career episodes more challenging without workplace experience from which to evidence the competencies.
So, do they give skill assessment for experience less than 3 years or not? Subclass 189 for instance require skill assessment from their authority (like Engineering Australia).