Asking my prof. whether he is affected by the hurricane in Texas, I and our security guards have not heard from nor seen a prof. of mine who I do research for.  We do know that he is from Texas, but we are unsure of his exact hometown.

How can I email to ask about his and his family's safety without overstepping any boundaries?
It's fine to ask. Like a commenter mentioned, probably better to not add that it's because you haven't heard from him on a particular issue (i.e. not "Did you forget those TPS reports, or are you affected by a hurricane?").

Some things to consider:


It's possible you haven't heard because he is directly affected: stranded, injured, hospitalized, dead.
However, it is also possible you haven't heard because his family is directly affected. He might be searching frantically for them, trying to make contact, helping in some way, etc.
Lastly, it's possible that the situation is completely unrelated.


With all of those things in mind, especially #2, a polite show of concern is certainly appropriate, without any attached expectations or requests. Something along the lines of "Since I know you have ties to Texas, I hope you and your family and friends are safe." Even if it turns out he isn't from the Houston/gulf coast area, there is a reasonable probability that he could know someone in the area and would appreciate the sentiment.