top operator,
AIP describes the situation you're asking about in ENR 1.1 para 59.2.
Here's the link:
http://www.airservices.gov.au/public.../1_1_1-116.pdf
The short answer is no, the normal circuit departure rules don't strictly apply if IFR departing via a SID from a CTAF. Of course, if you are IFR in VMC and there is lots of circuit traffic, you could elect to turn with the circuit direction and depart over head. Or just broadcast your intentions to fly the SID on CTAF. Also, for IFR traffic purposes, ATC should be advised if you're flying a SID and won't be established on track within 5nm of the aerodrome
If you really need to fly the SID, you are probably in IMC in which case circuit traffic isn't a player anyway.
VI