Absolutely! Web developers build out websites using a CMS or an application framework while engineers write and maintain the code behind the CMS or framework. Simply put, engineers build the tools that web developers use to build websites.
Why does this matter? If you are designing a new website that has complex functionality a web developer might give you the impression they can handle this workload, but in the end they cannot. They will either have to source that part of the project, try to pull in modules from the community that somewhat accomplish what you need, or worst of all leave you there with nothing and walk away from the project.
The ideal scenario is a company that has a good combination of both engineers and web developers.
Having a nice balance of website developers on the team helps to keep the project on track and on budget. Every project has basic templates, plug-ins, and tasks that would be overkill to have an expensive engineer work on. Allow the web developer to bring things as far as they can and then pull in the engineer only when needed to keep costs down. Web developers will also help to keep the project on track. The engineer can often times be a bottleneck in the project as they are pulled in several directions throughout the company. A web developer can help alleviate this bottleneck by taking on trivial tasks throughout the project. And let's not forget about attention to details. Something in the DNA of an engineer only allows them to get things to a functional point and then it's time to move on. A web developer will pay close attention to usability and presentation before release.
Having engineers on the team ensures there won't be technical constraints or limitations. There's nothing worse as a client when you hear the phrase, "you cannot do that", or "the CMS doesn't allow us to change that", or "I did not write that module so there aren't a lot of customizations available". The engineer likely has access to all the source code and should be able to adjust whatever's needed to get the job done. This isn't typical for basic marketing websites, but should you be ahead of the curve and looking to conduct business online you're going to want an engineer on your side.
A good way to confirm a company has engineers on staff is to ask if they have written and/or are contributing to any CMS projects (open source or proprietary). If they are not contributing to the community and are only taking from it, there's a good chance there are no engineers in the building. Depending on your project this may be just fine, but it is something to be aware of if you plan to scale your operation.
Another effective way to ensure engineers are on staff is to take a look at their portfolio. If there are portfolio items, case studies, white papers, etc. available outlining work similar to what you are looking for, there is a good chance you'll be in good hands. As precautionary step, be sure the parties involved in the portfolio project will be available on yours.