Is creative writing needed to be a graphic designer?
I want to be a graphic designer but I'm awful at writing copy, editing, coming up with slogans and catch phrases.
Do I really need to learn Writing, Spelling and Grammar and such to be a successful Graphic Designer?
Required? No. The larger the company, the more likely it is that they'll have specialized departments for certain jobs. Marketing is a skill, writing is a different skill, graphic design is another skill, web design is a specific subset of that skill, programming is an entirely separate skill.
If you can write, great. In a small shop, that will help you get hired. If you can't — and by that I mean "write creative business copy," not "basic spelling and grammar which showed you graduated high school" — it shouldn't hinder your general employment chances.
In part, yes. As an expert, heck no.
Writing is its own profession. You don't need to be an English major or writer to be a designer.
As a designer, I am often asked for ideas, i.e. slogans, tag lines, phrasing. But this is always done with professional writers so they have the final word on what will be used. While a client may pick my brain for creative ideas, I'm not asked to actually cement any idea myself. A writer always reviews everything before design begins.
That being posted, you do need to know how to spell, as well as have at least some basic idea of grammar and usage. You'll still be called upon to input headlines or small amounts of copy and spelling inaccuracies can be problematic.
95% of the text I use for designs is provided to me by clients or writers they have hired. While I may make suggestions or be asked to change a headline here or there (which requires typing) for the most part I don't input a great deal of text myself. I certainly do not advertise or sell myself as a creative writer capable of constructing original copy for clients. I refer client to actual writers for that stuff.
Writing is a lot like printing or web development to a designer. Yes, you should understand the basics, be able to handle rudimentary adjustments when needed, but you don't need to be an expert by any means.
Past companies I've worked for had dedicated marketing, dedicated editing/writing, and dedicated design departments. Many of the larger companies I freelance for today have the same structure. In larger corporations, they tend to understand that like design, writing is a specialized area requiring specialized skills. Writing is closely tied to design, but in my experience few designers are also asked to be writers.
It's only with smaller companies where a designer may also be asked to be a writer in an effort to save money and streamline their own outsourcing. Similar to how smaller companies want a "web designer" to also code everything and build their back-end database -- two jobs, but if they can hire one person and only pay one salary, they certainly will.