If you're incompetent, yes.
Sólo si lo eres.
No, not knowing what you're doing with the software will make you look less professional. And if your employers or superiors are aware that you don't use the proprietary "industry standard", they might even respect you more for being a risk-taker.
The quill pens used by Leonardo were not made by Adobe, so his works weren't really professional?
No. See http://libregraphicsproduction.com/.
Bad designs will make you less professional. If you care about tools and not about design you will not be a great designer.
That depends on your definition of professional!