I'm afraid I don't completely understand the questions, but here goes....
1) I'm not sure what "object oriented" really means. Other people more familiar with the term would be able to help more than I can. AutoLisp can certainly do many things that are not specific to "objects," so the answer may be No, but many of its functions do work on drawing entities, if that means that the answer is [partially?] Yes. Some drawing entities represent "objects," but many do not, if that suggests an answer.
2) What do you mean by "in main program"? In AutoCAD, yes, you can define functions [that's one of the main things AutoLisp is used for], if that's what you mean, but usually by way of something else, such as a text editor outside AutoCAD, or the Visual Lisp console [VLIDE], which operates from inside AutoCAD but has its own distinct way of working, so it's not really "in the main program" in the same way as other operations. If you mean "Can I add a function into the 'core' AutoCAD program itself?", the answer is No, but you can make your own functions and commands, and have them automatically loaded in every drawing, which should be effectively the same.
3) Does the word "not" belong in that question? Assuming it should not be there, the short answer is Yes, but by "function" do you mean AutoLisp's internal functions themselves, or a function defined using AutoLisp? Yes, you can call AutoLisp functions from within other functions -- a very simple example:
(setq Point1 (getpoint "\nPick point: "))
And you can call functions defined using AutoLisp [with the (defun) function] from within other functions, by putting the defined function's name in parentheses.
Go to the Customization Guide and some of the tutorials and website links that you will find with a Search as suggested before, and put some time into it, and your basic questions will be answered.
Kent Cooper, AIA