LabVIEW
Labview 2017 - Centos 7
I mean, 2017 is probably better than 2016, so if you're buying it, get the new one. I just meant, if you're using a demo, probably most people on the forum can't help you. I think speaking with Sales is the way to go.
NI-VISA definitely is required but I would expect the Initialization VI to already generate an error if it wasn't. Might still be a problem with a incomplete or corrupted VISA installation.
As to the necessary VISA version, it doesn't really have to be the same as the LabVIEW version. They are very much independent of each other so just about any NI-VISA version for Linux, which isn't ancient, should work.
No, VISA definitely doesn't automatically append <CR><LF> to a message, Windows or not Windows. You can configure it to automatically append <CR> or <LF> to outgoing messages, but it doesn't do that by default.
A timeout error on VISA Write is very rare and usually indicates some problem in VISA to interface to the underlying serial port system API. It can happen on Windows too, with some less than perfect COMM drivers, especially with low cost USB virtual COMM interfaces.
Sounds familiar. Had similar problems with the NI Linux RT system on cRIO platforms. The reason most likely is that the user who you start your LabVIEW session in doesn't have the right access rights to /dev/ttyACM0 when using a USB to RS-232 adapter on there. And this is not a VISA problem in fact but more a problem with how the Linux device driver system is setup. And to make it all more interesting and because it is Linux, there are of course several different systems of autoinstalling device modules when pluging the according hardware in. And each Linux distribution has its own preference which of these systems it likes and when it will switch from one of them to another between releases. After all this is all Linux, with the freedom to develop a new subsystem for a problem, rather than resolving that problem in the existing subsystem, since that subsystem wasn't developed here and uses the wrong shell, script language or intention style! 
<irony>Or the new developer simply doesn't like the original developer for their hair cut, skin color or whatever else!</irony>
You will have to find out what auto install module subsystem your distribution uses. The two I have worked with in the past are the older mdev system and the newer udev one. They are similar in what they do but use slightly different configuration files and approaches. Most likely you would use udev nowaday, unless Gentoo has for whatever strange reasons some direct mdev involvment and prefers to go through the troubles to replace the kernel default udev with this one for their distribution.
This post is for the cRIO system from National Instruments but applies to other Linux installations as well for the most part. Since your device is an ATmega based USB serial port you will want to look at the ttyACMn related changes.
