Some children older than your son would have a hard time. Some children younger than your son wouldn't miss their mom's (even very attached, constantly nursing kids) much at all.
How do you think *your* son will react?
DD spent the night with her Nana & Poppa at almost 3.5 and she did great. She was not night weaned at the time. But she *really* wanted to. When we called the next morning she actually put the phone down w/out talking hoping we would just leave her alone
DS was younger when he spent the night with Nana & Poppa (and sissy). He was still nursing every 1-2 hours during the night. He also wanted to. The both went to two nights of Grandparent Camp last summer (6.5 & almost 4--- going 4-5 hours once a night, still nursing 5-8+ times daily) and they both loved it. SO, I don't think seperation at that age, even if still nursing, needs to be traumatic. BUT, I very much wanted it to be a choice on my kids part.
Have you asked your DS? What does he say? Is there anything special your DH could do with him that weekend? Maybe even start a tradition!