As someone who is involved with hiring UX designers and researchers, a UX certification on a resume doesn't impact my review of a candidate. The single thing that I'm most interested in is a candidate's portfolio, regardless of their level of experience.
When I review the resume of a fresh college graduate, their college degree is useful to see (a degree in design, HCI, or CS is most likely to be positive, but very few degrees would be negative; also, a MS or MA is more positive than a BS or BA). In their portfolio, I want to see what UX work they've done (class projects, internships, other jobs, volunteer work, etc) and where their UX interests lie (research? design? big data? mobile? ... ).
When I review the resume of someone who is experienced in UX, I glance at their degree, but their degree has a much smaller influence than it does for a fresh college graduate. For someone with UX experience, I only care about what they've done: what they have accomplished, what constraints they were under, what they did well and what they didn't do well, what they learned from those projects, etc. I'm also looking for someone who can show me how they have grown in their career, such as taking on larger UX projects, mentoring other employees, presenting public talks about their work, etc.
When I review the resume of someone who is experienced in another field and is looking to switch to UX, then I look for a portfolio that shows me how they either made UX a part of their current role or did some UX work on the side to build up their portfolio. I also want them to be able to clearly explain to me why they're interested in moving to UX now, and how what they have learned in their positions to date will help them bring a unique perspective to UX and to the position that I have open. For example, someone who has done marketing work and has gone back to school to get a UX degree should be able to tell me about how brand and UX are related. A developer should be able to tell me about how their deep technical skills can help them be a better researcher or designer. There are lots of relevant and important skills that you can learn in other fields, such as communication, presentation, influencing, ability to manage multiple projects simultaneously, and so on.
There are a few things outside of your portfolio that will discount you in my consideration. For example, lots of typos or a poorly-formatted resume is a bad sign, because it tells me that you're not detail-oriented, and a lot of great UX is in getting the details right. A cover letter that is generic and doesn't discuss my company, the position that I'm hiring for, and how you are a great candidate for that position based on the items that are listed in the job description is also less likely to get my attention. A generic cover letter tells me that my position wasn't interesting enough for you to expend sufficient effort to customize a letter to me, and so I'm probably going to spend more of my energy on someone who did take the time to explain exactly why they think they're a great candidate for this particular position.