Can a 90 watt halogen bulb be used in a recessed lighting fixture instead of a 75 watt incandescent bulb?

Absolutely not. A halogen lamp IS an incandescent lamp. And 90 watts is 90 watts.

Well lets see now.

What is the max wattage of the fixture? Are the connection the same for both bulbs?

Normally because of the damage heat can do to a fixtures wiring, you do not exceed the max wattage of the fixture.

That's why you should never replace a 40 watt bulb with a 75 watt bulb on a 40 watt fixture. Heat is the enemy.