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I am surmising that the software is open and as long as your written software part is made available
AFAIK, as long as you're willing to provide the source code of your entire "project" to anyone, you should be fine. I'm not sure about the status of keeping code private between the producer and the actual customer.
The complications arise when you want the software to be "proprietary" (non-open), something a lot of developers of "professional projects" would prefer, for various reasons. Various Arduino officers have said they allow such proprietary code using the Arduino core libraries, but that's not what either "GPL3" or "GPL3" (which authors have slapped on various 3rd party libraries) says, and even the LGPL license used by the core has "difficulties" with statically-linked deeply embedded microcontroller software. If you work for a company with lots of lawyers, you are likely to face barriers to using Arduino libraries (I'm sure that RMS is really proud of keeping so many lawyers employed. :-( )
In the absence of lawyers, a company with a project using Arduino libraries might be faced with paying "other" license fees, or with releasing their "private code" as open source.
For example, right now, I'm looking at the EtherCard library for ENC28j60 Ethernet/ip/tcp. It's all GPLv2, which I interpret (I am Not A Lawyer) as meaning that you can only use it for open-source projects. I find that annoying, and it makes me feel like not wanting to make improvements to the library :-(