Should I learn to use Emacs with no intention to learn Lisp, if my other option is to get familiar with vi?
I know little Lisp and use Emacs to edit my C and OCaml programs on windows and linux.
Well, if you don't want to customize your Emacs, you won't need Lisp, either. And you can also do some basic modifications using the build-in customize functionality and by copy&pasting code of others. But truth being: I have written several hundreds of lines of code to customize Emacs to suit my needs. On the other side, as far as I know, vi is not as customizable as Emacs, so in the end it is probably more about what editor you like more and you should try both.
Why not?
You can still learn vi (probably vim or elvis). You can learn jedit. Or nano and pico. Or whatever other editor/environment/language-host you fancy.
Why put such an arbitrary restriction on things? While your emacs experience will be better if you learn at least basic elisp (a ... derelict ... lisp implementation), it's not required. But at the end of the day, it's a tool. Get as many useful tools as you can. "Usefull" also really depends on context.
Configuring Emacs is a journey, and it's something that you're going to want to do. Being able to customize your developing environment is one of Emacs' greatest strengths. It's almost unavoidable. You pick up bits and pieces just by looking at other people's .emacs files.
Knowing just a little bit of Lisp goes a long way in Emacs.
Yes. With all the resources out there (FAQ, Emacs wiki, SO emacs) and custom (M-x custom). You don't need to know lisp, you just cut/paste what you find.
You can drive a Ferrari/Yugo without knowing the internals of the combustion engine or how a formula one transmission works...
I have used Emacs for several years with next to none knowledge of Lisp and it served me well for all of the projects I used it for.
You can always simply assume that the configuration you're writing is not in Emacs Lisp and that it is just some funny configuration format - there a lot stranger examples out there(such as sendmail).
I should warn you though that once I started learning Emacs Lisp my Emacs mastery expanded extremely rapidly - now that I understand the details of the language I can easily bend any configuration to my needs and more importantly I started writing my own extension to Emacs, which add to it even more capabilities.
If you decided to start with Emacs I recommend to read first this great book - it taught me a lot of things for Emacs at the beginning and it assumes no Lisp knowledge. It won't teach you any Lisp either. Afterwards my advice would be read the official Emacs manual and start exploring the Emacs Wiki and #emacs on freenode.
Learning Emacs truly is a journey, that is not for the faint of heart, but it is journey that is most certainly worth it...
You don't need to learn Lisp to use Emacs. Even basic customization of Emacs works fine without Lisp knowledge. If you need something beyond your capabilities, there are many helpful Emacs users.
Learning a bit Emacs Lisp will later enhance your understanding of Emacs.
Emacs Lisp is a relatively simple Lisp dialect. Basic Emacs Lisp is not that difficult to learn. As an experienced Lisp user I have to say that Emacs is available quite some time and the users have written some amazing things in Emacs (like org mode). Some of the Emacs extensions are very very well written and it is a pleasure to read the code.
I've been using Emacs for a year and a half, and really only picked up whatever elisp came without trying. I have a heavily extended set of configurations (first in a .emacs file, now in ~/.emacs.d/init.el and friends), which are totally a result of cutting and pasting from the excellent resources found online. Aside from, of course, the EmacsWiki, you should see the fine Emacs Starters Kit and subscribe to Planet Emacsen --- preferably in a feedreader. It's prettier.
Having said that, after you have a working setup you might yield to the temptation to learn a little elisp. I've just started the free Introduction to Programming In Emacs Lisp, which comes with Emacs and is best read from within Emacs Info. It assumes neither programming ability nor lisp knowledge, and is a friendly introduction to the 'vibe' of emacs lisp which I find to be well-written in the extreme, friendly and concise, and worth 10x every minute I have spent with it.