Are 3D printers efficient for printing a detailed iris to bypass iris identification system?
I take lectures in university and was asked to read a review paper on 3D printed organs by Anthony Atala (the most famous paper in printed organs research). The paper discussed about using several techniques to print the tissue we need at functional resolution. The review also cites detailed procedures to 3D print lung and skin tissues.

Coming back to your question, we have reached a point in time where we can scan a real Iris and print them! Yes. And people use this technique called self assembly to achieve this (Other design approaches like Biomimicry and MiniTissue assembly is also being used right now). To do this we first extract cells from the donor. Or We do a functional high res scan of the extracted cell/part that we want to replicate. This is done via FMT-CT-Fluorescence Imaging, etc. And we cultivate the cells in bio incubators (we can also print cells btw - If the exact environment and operational conditions are maintained, we can print cell-replicas that will later self assemble to form the Iris with the same resolution and functional properties as that of the real one). The cultivated/printed cell is used as the tissue forming material. Forming is done by the cells themselves and is thus christened Self assembly.

Although this may sound futuristic, Autonomous Self Assembly is something that's already being done in Labs! The method works by studying embryonic organ development. For instance, Early stage cellular components of a developing tissue makes their own ECM. Like mentioned before, if we use proper signalling, and environmental manipulation,  we can create autonomous organization and patterning to make something we want. Advantage of this method is that we can work without scaffolds. This method relies on cell as primary driver of histogenesis. Knowledge of how an embryo grows into tissue (embroyo tissue genesis and organogenesis) is applied to achieve "real" cell dimensions/properties.

I would recommend you to read the paper for detailed information. The method I mentioned in this post is only one among three other methods that are being used currently in this domain.

So yeah. My answer is yes. You can print an Iris and fool the system.

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Updates


S. V. Murphy and A. Atala, “3D bioprinting of tissues and organs,” Nature Biotechnology, vol. 32, no. 8, pp. 773–785, Aug. 2014. DOI: 10.1038/nbt.2958 
Withdrew my claim "any given resolution"
Details of the process