I believe that the guidelines are very firm - and with so few children available to adopt, perhaps there may be some issues - but why not face this head on and ask the department?
You arent on their lists yet - so why not make some enquiries and be very honest about your concern?
Mental Health is no longer as stigmatised as it once was, and many people find that with the right treatment plans and support, their health is great. If that is the case - and you have evidence of this as life goes on - I would *hope* that you as a couple wishing to become a family *should* have as much chance as anyone else.

The departments stance on it all is most likely that they want a secure,loving and stable home for a child - so if anything *may* get in the way of that - it may sway decisions. Not sure. Ask them?
Good luck.