Hi Danner - I'll take a stab at clearing some of this up for you...
First, to define
PC Access, that is the HAI tool to PROGRAM your system. It is available in both End USer and Dealer versions. You can see the differences at the link. I am guessing since you are a technical person that you want to be more involved with your system (as a DIY) rather than just having a Pro install and support it. If that is the case you will need the Dealer version of the software so you have full access to all the programming. This includes all the security settings, automation logic, etc. So this is required to setup any panel for use, it is not intended for CONTROL per se.
So now you mention 'control your automation system via a mac'. That can mean alot of things. For many the OmniPro II alone is your controller and no mac is ever needed, The OPII via its automation logic can probably do most if not all of what you want. An external software based system is only needed to do more of the 'fluff' and not core automation. Maybe things like weather, full Text To Speech and other types of things. Some people supplement their panels with software systems like CQC, Homeseer, Elve, etc. to get these other functions.
More to the 'control' aspect I think is really more the 'interface' or how you will interact with your OPII. There are several ways to do this. You have your basic HAI consoles, then HAI has their own touchscreen interfaces like the 5.7e and others which is configurable with their automation studio. They also have iDevice based control interfaces like their SnapLink. You can see all of that stuff by navigating around the link above. So, you could have a complete solution with interface directly from HAI.
Where 3rd parties like NullRiver come in is they offer either replacements and/or extensions to the HAI offerings. For example the original Haiku is similar to HAI SnapLink mobile in that it allows you to interact with your system via an iPhone/Pad. Many will argue Haiku is a more complete product but that is a personal decision. So then came along HaikuHelper which sort of complements Haiku and extends functionality of the core HAI offerings, similar to what CQC, Homeseer, etc. do. HaikuHelper is not needed for your core automation or interface/control. It's only needed if you desire to have to of the extra abilities which started with things like time sync, energy cost sync, notifications and climate features. The latest version expands further into including a complete API which will allow you to create your own HTML interfaces, etc.
Personally, I see HaikuHelper at an early stage pro level system for the mac. It is not really at the level of a CQC/HS/Elve in that they don't have their own touchscreen interface GUI designers, but rather give a developer complete control via web development. They also don't have drivers to things outside of the OPII for things like Caller ID, etc. So, if you strictly want control of your OPII Haiku and HaikuHelper are a great way to go and I imagine Helper will continue evolving and growing. If you needed more advanced 3rd party type stuff you would need to explore some of the other software options like Indigo, Misterhouse, etc (mac based). See
this list. I would like to see Helper evolve into a complete system with some of these other drivers, etc as well as perhaps wizards or GUI program control, but as a pro developer Helper is right up your alley.
I hope that helps at least a little...