KLM sold me a flight from Venice to Houston that changes planes in Amsterdam.
Should I be concerned about the layover time?
There is only one hour to get from first leg flight over to the second leg flight.
What is the airport situation. I think I clear security and immigration in Venice....
Please read my posts in this thread; https://community.ricksteves.com/travel-forum/general-europe/help-a-newbie-understand-flying-overseas-schiphol-airport
You’ll find everything you need to know about transferring from non-Schengen to Schengen at Schiphol Airport in that topic, but the same applies when you travel in reverse. This means you will leave the Schengen zone in Amsterdam and that’s where you will go thru passport control.
I think I clear security and immigration in Venice...
You will have to go through security in Venice, as with any airport.
Your Schengen zone exit processing ( passport check) will occur in Amsterdam as that is you departure point from the Schengen zone.
AMS has a reputation for efficiency, but an hour is a 'no flubs allowed' situation. Be sure your running shoes are laced snugly. Use the restroom on the plane before landing at AMS.