I guess so they should have mentioned something very business-like of both of them getting tested just a couple of lines, nothing preachy.

The movie put it in such a manner that the guy was so filthy rich, I don't think it mattered.

This message has been deleted.

During oral?

Doggy dolphins?
Erection?

Yes they did have that conversation. The film was all about a billionaire who had the money, time, inclination, stimulus and right people with whom to play mind games.
As to the OP's question, for the answer you'd probably have to ask Gage, Diana or possibly Jeremy.

I agree. It was less about paying for the sex and more about testing them to see what they would do with the offer.
I haven't seen the movie years either. But I thought there was a conversation about everything having a price. And the Woody Harrelson character claiming it wasn't true or something to that effect. That the Robert Redford character was attracted to the wife was kind of secondary to the offer. I think people distracted by the sex and money part.
"I am allowed to think everyone is stupid for 10 minutes." Randy Susan Meyers

Using a condom does take away a lot of sensation.
But I guess that death takes a lot more.
Haven't watched the movie in a while, perhaps there is a dissolve
that could mean that some time had passed enough for her to
get on some sort of birth control.
Paying that amount of money for 1 night with any woman sounds ridiculous
even today over 20 years later perhaps he did use a condom and what
he really wanted was to screw with them psychologically more than physically.

Not all women can take pills or use other hormonal forms of birth control. Also, there is a waiting period of 30 days before pills become effective and even then it depends on where you are in your cycle before you can start to take them.
From what I've been told, the use of a condom doesn't take away from "the pleasure" if you're using the right size and know what you're doing.
"I am allowed to think everyone is stupid for 10 minutes." Randy Susan Meyers

Maybe in the contract there were details that she had to take pills both of them screened for STDs and also in case that she got pregnant (even with the pills) he wouldn't be held responsible.
If he's paying that amount of money I guess that he wants all the pleasure he can get out of the services she will be providing.

Why not?
1-I doubt he'd want to have to pay child support to what was supposed to be a one night stand.
2-Pregnancy isn't the only thing to worry about.
If you can't walk and talk/text at the same time, do the rest of us a favor and get out of the way.