It is absolutely 100% allowable. Back in the day, when my husband was a boot, they got 24 hours off base liberty. I lived in NJ at the time and I picked him up on base and we had a really great night together and with his other shipmates. As a matter of fact at sometime around 4 in the morning our hotel room door flew open and someone yelled "FIRE FIRE FIRE Get up NOW!" Jim jumped out of bed at attention and then realized where he was. He turned and looked at me... I said just come back in a little quieter please. They were off, banging on other doors to see who they could scare out of bed. Now that is boys will be boys fun!
What you can't do during off base liberty is get drunk, show public displays of affection or in any way be disrespectful to the uniform. They are expected to maintain as they have been for the last 7 weeks. So yes, visiting with them during off base liberty is totally acceptable.