Can a Unity pro user work in a team with people using the indie version?
Yes.
However if he provides pro-only features to the rest of the team 
This represents my own opinion and is not legal advice.
Thanks you, I will keep on this thread and await more information regarding this, since it is quite a gray area.
It’s not really a gray area. Check the EULA-
Yes i see that as meaning NO!!! they gotta make their money somehow and if anyone could form a team and have one person with pro doing all the pro stuff to it then building the game on that then they lose out on money. Now i think they should have something like sits but they dont and its their Engine so its their rules sad but true
It’s unfortunate, since artists and designers usually don’t have to do a lot of critical work. A bulk of the time we’re just previewing assets and scripts and don’t need the full power of a Pro license. Even Torque was better in that respect, at least the previewers come for free. I think even Unreal engine might allow use of UDK alongside licensed seats, even if you’re better off using an internal build.
The EULA does not say ‘team’, hence it is a grey area.
As long as you’re not trying to rip Unity off I doubt they’ll have an issue. But as I said earlier, that’s opinion.
unless you are registered as a company, a team counts as individuals. Now i doubt they would care unless you are making money. so here is what i think you could do if you must mix pro and indie, work like that till you are going to sell then before you sell buy everyone pro either by getting funding or what ever.
What if im the only one using the engine? And the others create such things as models and textures. Do i have to pay them all pro?
I do not think anyone not using the Engine has to get pro its only the people using the engine witch will be basically getting to use pro features free. but what i would do is send unity an email as they do respond with answers to any questions you have.
I think they should offer an option to buy pro with seats so you can give your team a spot then when they leave the team take it away kinda thing… but they dont
what you could do is buy as many pros as you need then get a contract that stats that as long as you are part of this team you can use this but only when you are part of the team or something like that.