Who knows if is possible to use these boards in a industry plant? Is possible to certify a machine using these boards? (CE for example here in Europe)
Most likely no, usually components that can also be used individually, need to be certified, especially electrical ones. So to certify a machine with drives an motors, they should also bear their own CE.
To certify the drives, you have pretty much 2 options.
1. You do it on your own.
This is quite a big task, the only "difficult" one will be the EMC stuff, you need a radio room, you can find example in some universities etc. and then you need to fix your mistakes. Don't worry there will be mistakes and shit to take care of.
The other stuff is more documentation stuff like, manuals (EU is a bitch as technically the CE requires manuals to be in the target country's language, so in most cases english is not enough), risk assessments etc. This takes a lot of time and a lot of effort.
2. You give the task to a company like Intertek, TUV...
I have always gone this route, expensive but then you get all CE, UL, CSA done at the same time and you are somewhat covered as someone else signs your work. Even in this case the EMC is always done before in another place. Some schools example rent those radio rooms out 10x cheaper what the time at intertek costs. So you try to do everything that you pass all the radiated and conducted emissions at the final test site. This will save you thousands.
3. Mix of the 2, you do it on your own and get someone to consult and help.
Probably cheaper than example the intertek route but a lot of work.
Some of the directives related to servos would be:
Machinery Directive
2006/42/EC
EMC Directive
2014/30/EU
Low Voltage Directive
2014/35/EU
Then most likely ROHS and REACH (but I think its hard to buy components now days that dont comply to both).
Then to find the subsections from those, I would ask someone that actually knows about this. Or see from any "major" brand like yaskawa, panasonic, mitsubishi, siemens... and just go with what they certify with (they will all have them on the manuals).