two varieties of tomatoes in one greenhouse

I don't think cross pollinating witll affect this years toms, but if you keep the seed to sow next year, you might not get them coming true.
I'm not sure how likely tomatoes are to cross pollinate. I have a vague recollection that some varieties or types are less likely than others, though.

Tomatoes self pollinate....it is very rare for cross pollination to occur, so don't worry.
Even then it would only effect any seed you saved to grow next year, not the taste of this year's tomatoes