Are they creating it for you or are they creating it for themselves (use your content with their advertising)?
The main question is do you NEED an app? I've pointed out here and elsewhere about so many companies creating apps (or sheepishly following other fads/trends) just because "everyone else is doing it." Is an app going to provide additional functionality to users that they can't get from a mobile version of your site?
If you've made the decision to do an app, then it comes down to one issue: do you have the internal staff with the skills required to create an app? If so, then there's not really any reason to outsource it (unless they don't currently have the bandwidth to work on it because of other projects).
If you don't have the resources in-house, then does it make sense to hire a new permanent employee to do this? Will you be making additional apps, or just this one? Will it require ongoing updates/maintenance.
Depends on several factors - what are your own skill levels - could you build your own? What do you want your App to do for your site and for visitors? Can the developer demonstrate Apps in use that they developed to do what you'd like? If having the work done will do what you want at an agreeable price, it may be worth it.
What about App maintenance and updates? Like any job you want done, it is good to shop around if you don't know the individual or business and have a clear agreement before starting. If they are using a publicly available RSS feed, the only disadvantage evident is that it does not offer anything new to your visitors - only offers a different way to access your site content. If the reason for wanting it is user demand, then it can be a good thing.
I tend to allow 3rd parties to provide source code for parts of an app, then merge them myself within my own dev IDE. By doing this no one company knows what the full app will be, and I retail full control over the end product.
I mainly use Appcelerator as my IDE, and find developers who use the same SDk. By having one developer create part of the app and others creating other sections no one developer sees the "bigger picture".
Even if the app will run on web services I spoof these on a made up URL with filler content.