Hi,
It is possible indeed to build something with playmaker without scripting. With EZgui tho, not at all, you will need control it somehow (with playmaker or via script).
It really depends the internal complexity of what you are trying to achieve really. Anything above medium sized project will require scripting, be it playmaker custom actions.
The very odd thing is that playmaker allowed me to accept and build projects that otherwise would have been simply impossible to achieve in pur script, all that in a natural/understandable/manageable way. This is somewhat contradictory with what I want to say, because I would be very very cautious about the lack of scripting knowledge. You should really have a descent understanding of scripting and algorithm design, otherwise you will hit trouble.
I'd compare this with Engineering software: they are really really powerfull, but if you don't how mechanical parts works, how they physically behave under strength and all that, you won't be able to achieve a descent result, and might even end up with something that is not feasible; In game it would translate into an application that simple doesn't work, or is not stable, and doesn't meet the client requirements. Such powerful tool are only tools, you need the basics and the experience to achieve something descent with it.
I guess the bottom line is that you need to take the best option available to achieve the result. 99% of the time, playmaker will be that best option, but for that last percent that is so specific to your need, you will need to script it.
Bye,
Jean