So far all my characters have been agnostic about the Maker. They have all been elves. Two of them started off believing in the elven gods, whilst the third was a bit of a rebel who largely took the Morrigan view of things. Having been through the Temple of Mythal, reading all the lore there, spoken with Abelas and then met "Mythal", the original believers are now former believers, whilst the other guy feels pretty smug.
One of them was opened minded about whether the anchor came from Andraste/Maker although she still wouldn't profess belief in the idea when quizzed by Mother Giselle after escaping Haven (so was established as a non believer), the second kept denying the idea that it was Andraste and so when it was revealed in the Fade what really happened, largely wanted to say "told you so" but instead had to be content with "I knew it was just me acting on my own". The rebel though took a different line and claimed to believe in the whole Herald thing (so was established as a believer even though he wasn't really) . This was fun from my point of view since I got different options at times as a believer and amusing for him since he was basically thinking "if the Maker doesn't like my false claim to belief, then hit me with something", which of course the Maker never did. After discovering the truth in the Fade he wanted to come clean on the issue but Mother Giselle insisted it would be a bad idea, so everyone still thinks he's a believer and after he declared "I'm the Maker's chosen" to Cory before stomping him, I don't think that's going to change any time soon.
My biggest issue was with Sera because she seemed to equate acknowledging that what Abelas said as being true with actually believing in the elven gods as gods. To my mind this is the whole point. I can acknowledge that there have been entities that their followers regarded as gods and which did seem to demonstrate power beyond the mortals around them and therefore I believe that they existed and were not simply made up. However, I do not Believe in them if that equates with saying that I worship them as gods or acknowledge that they are actually gods that created the world, have an overall influence on the cosmos, etc.
So, yes, I think you can be an agnostic about the Maker or in fact all the other "gods", depending on what you idea is of what a god should be. It is probably a good idea not to be totally atheist just so you don't look stupid if the Maker suddenly appears.
It is also worth noting that if you believe in the Maker but not the other gods you can still be described as atheist. The Christians were called atheists in ancient Rome because they would only acknowledge their own god and not any of the others.