Is adding two vectors in roblox the same as in unity?

Vector3.new(1,1,1) + Vector3.new(1,1,0) = Vector3.new(2,2,1)

Vector3.new(1,1,1) + Vector2.new(1,5) = ! ERROR: incompatible types !

CFrame.new(1,1,1) + CFrame.new(1,1,1) = ! ERROR: no !

CFrame.new(1,1,1) + Vector3.new(1,1,1) = CFrame.new(2,2,2,0,0,0,0)

list of more possible operations using coordinate frames: http://wiki.roblox.com/index.php/CFrame#Operators

list of more possible operations using vector3s: http://wiki.roblox.com/index.php?title=API:Vector3#Operators

good to know that when using vector3s, or CFrames, roblox measures in "studs", so 1 stud^3 would be a full block

and the annoying part about vector3s is that setting a parts position, "Orientation", or size, it has built in collision detection, so teleporting a part inside of another part is way different from using Part.Position than Part.CFrame

The simple answer is no. Roblox and Unity are two completely different engines of code, and Roblox is mostly pixelated, compared to a smooth Unity. Plus, they are two completely different dialects of Lua. Some of the code in Unity cannot be transferred to Roblox Lua or else it'll get errored out. Therefore, you cannot transport Unity code to Roblox.