You are right...it's not advisable to grant Administrator privileges to software from untrusted source....however, in this case, we are talking about software downloaded from trusted source, like Mimaki...and it's not permanent...it applies only to the software in question.
It's not so much as to if it's from a trusted source or not, but if the software has bugs that could be exploited or if the software that has admin rights does some type of write in a key system file that causes some hinky issues or even the software's own system file. Those that remember the 9x days, probably remember that.
Any modern software being written should allow for regular user use in day to day activities. If they are using legacy protocols that require perpetual admin rights to even just run their software, imagine what else is going on that could be exploited. If the computer is offline from a WAN connection, this is not as a big deal, but if it does have a WAN connection, I would keep an eye out on things. That's just me though.
Now the odds of something being used in Mimaki software versus macro exploits in Excel (by the way, those macro exploits are viable on Macs as well), probably not that high just due to user pool. I'm just one of those when one starts to be lax in one area, it tends to spill over into others. I'm sure that there are plenty of people that only have one account on a Windows computer and some may not even have a password to that.
This may be the only way to get the system up and running for this case, not trying to say that it isn't, just be careful, especially if it has access to a WAN.
