With any of the job search engines including Simply Hired, Indeed, Juju, etc... the main barrier to inclusion is usually having a well-formed site and a feed of your jobs (in XML format.) If you have a feed, your site should be able to be included fairly quickly.
With that said, your site needs to have quality job postings. Don't mix jobs with other classified ads.
Above all, you need to have unique, quality job listings.
Assuming the above, setup your XML feed and submit it via the method each engine provides. Start an advertiser account too! Why not try it, at least? Driving traffic at a small per-click fee is good for your site's advertisers and for your overall traffic - you'll find the ROI to be exceptional!
At the least make sure your jobs are unique and offer access to postings that these job search engines couldn't get to if they didn't accept your jobs. All job search engines want to be as comprehensive as possible. If you have good real jobs, they will want to index them for their users.
Make sure they can determine that your jobs are good, unique and important for their users. And, again, make it easy for them to index them via XML.
Indeed.com, and I'm assuming SimplyHired.com as well, will add your XML feed to their organic listings in 3-6 months, unless you signup for PPC, then they accept your feed immediately.
Plan on spending a few hundred min. a month.
If you haven't had someone create a feed for you, I can do it for free, if your website is developed in ASP.NET.
If it's not, I would have to spend a little time learning how to do it.
I did my own and Indeed is waiting for me to sign up for a PPC account.
My feed is at www.findjobz.com/jobsfeed.ashx if you are interested in seeing it.
It has already been accepted by Indeed.com
I have a feed and have submitted it several times for the past several months. I have also tried signing up for an advertiser's account (several times over the the past sevearl months) and not hear back from SH. I don't know what they're doing over there, but it doesn't seem like their interested in new customers.
I can assure you that all of the job search engines are interested in new customers.
If your feed is decent, they'll accept you. If it's full of jobs that aren't unique (ie can be foudn elsewhere) they won't include you even if you're willing to advertise.
If your jobs are unique and you have a feed, but you still don't get any traction when offering to create an advertiser account, feel free to send me a direct message and I can take a look at your site/feed to provide additional advice.