Employers don't care whether you did combined LLB or grad law.
A plus for combined is that it saves you a year (especially if you want to do honours in arts). Negatives, you do loose 8 subjects...but saying that, if you know what you want to major in in arts its not that much of a loss. Its only 8 subjects all up over the course of the three years (which isn't heaps in the scale of things).
I guess a negative for grad LLB is that if you get into combined, its a hecs place, whereas for grad law there are also fee-places - so there may be less of a chance of getting a hecs funded spot if you did grad. (I don't think there are limits on how many fee vs hecs spots grad law degrees should have. It's up to the individual uni.
I think if you got into combined law straight out it would be difficult to say no to it, especially if you were set on doing law.
Saying that, I know combined LLB at usyd can be flexible - a friend of mine was officially enrolled in Combined LLB/Arts but couldn't do the undergrad law subjects (because her arts degree was on another campus), and they just let her defer all her law subjects and she ended up doing first year law with the grads. Not sure how common this is (wouldn't think its that common), but it shows its possible - if you have a good reason.