"The department has a new Assistant Professor who was hired last year. I plan to call him and chat him up, asking questions regarding his hire process last year and salary negotiation. Do you think this is OK?"
No. Do not do it. Don't even think it.
Re salaries and negotiation: It's possible faculty salaries might be publicly available, particularly if it's a public institution.
"Don't trust too readily when it comes to salary issues. People will lie about their salaries right to your face. This is especially true of your own colleagues who fears you getting more pay then they."
Let me point out that there are people who are uncomfortable discussing their salaries and that does not mean they view everyone as potential rivals, nor are they automatically saboteurs.
Oh. Lord. No.
I'm pretty open in general and have no problem helping someone with an offer---if they call me I'll give 'em tips on getting things I didn't even think to ask for. Its not me against Newbie its me for the Newbie against the institution! But, I would NOT be comfortable in the least having ex parte communication with an interviewee. The problems from that could be enormous for me but also for the candidate. You get the offer, then if you feel someone was particularly friendly on the visit and is very junior then while you are "thinking about the offer" you can contact to ask them what they think about things as new faculty and see if there is an opening for talk about *money* issues. If they don't give you one, I would not go there. Some people are "dogs in a manger" about money others are simply uncomfortable.
But do not ever contact some poor untenured person while you are a candidate. Both of you look bad.