I had just heard about hashgraph, but not paid much attention to it yet. As you are asking, I read the whitepaper to better understand the project.
They are quite secretive about the structure of the data : they run a pattented algorithm as it seems. Anyway, I don't think it is a DAG, as there are 49 consensus nodes that put timestamps on each transaction and seem thus to order them in a kind of chain. I have no particular opinion on whether this is a good project or not : it strives to be an efficient platform for dapps and could be a contender for EOS in that regard. They don't make any comments on IOT and I don't think it is well suited for IOT anyway.
The core value proposition of a DAG is that each new transaction validates two previous ones (and makes some little POW to counter spamming), thus avoiding the need of any consensus node and more importantly of any fee. This property is key for IOT to make business models relying on gazillions of transactions of very little value possible.

The only other project I know of with an ambition to be a general protocol layer for IOT is IOT Chain (ICT) a chinese competitor of IOTA (they use a DAG and anchor some states on a BFT blockchain). Pretty tiny today as for market cap but they work closely with hardware startups in China, have a solid team and are rushing to put their solution to market before IOTA becomes an indisputable standard (Fujitsu wants to make of IOTA the standard protocol worldwide for IOT... It could fail, but that speaks volumes about the soundness of the project)