It is noticable. I found myself picking out non gw models in an apoc game before. The old red shirt didn't care at the gw store. Anyway since gw don't make female guard other companies have female guard, etc. I personally don't have a n problem with it. If it is a tournament it should be Wysiwyg and look like it fit with 40k.
I do convert from other companies like Warmachine, but that's due to it being easy to bit order from them, so I do have a few heads and wings from hordes/ Warmachine