He will have a lot more social and business contacts, working in different offices.
If he has appropriate boundaries, this will not lead to cheating, if he does not, he could be in prison and he would still cheat.
It's really all about doing the work, having good boundaries, etc.
An example of someone who had very little social contact other than other women, was my FWS, she was a stay at home mother by choice, she was part of a mothers group, she had four small children with her most of the time. I was surrounded by almost exclusively female coworkers, of a variety of ages, many of them, single, divorced, and looking for something ( everything from NSA to marriage). I had lots of opportunity and never considered it. She took the first opportunity that came calling, and it did not matter that the kids were at the house.
I would suggest that you express your concerns, but that you also expressed that you support his advancing his career, but you can also make your boundaries crystal clear as well, whatever those boundaries are.
My wife has since returned to the workforce, by choice, but she knows what my boundaries are, she knows that any type of violation of trust means that we are done.