GATE Embedded and GATE Developer are licenced under the GNU Library General Public License, version 2 of June 1991 (referred to as "The GNU License" below). (We also use lots of 3rd-party tools which are licenced separately, but these licences are compatible with the discussion below.)
To cut a long story short, you can use our code freely in commercial systems, and many people do. A longer version follows:
Under the terms of the GNU License, the source code of a system that uses GATE as a library consitutes "a work that uses the library" and is therefore exempt from the terms of the license. Executables of embedding systems (that are linked with GATE code) constitute "an executable that is derivative of the library" and are subject to the terms of clause 6 of the GNU License. This clause requires that if these executables are redistributed they must include a copy of the GATE code (both binary and source), a copy of the GNU License attached to that copy, and give notice that GATE is used within it, partly by including this information in any display of copyright notices given by the embedding system.
If you modify GATE code, you must: clearly mark what modifications you made (e.g. in the headers of the files you changed), and you must make those modifications available free to anyone who wants them. This does not apply to work that is identifiably not part of the library, such as components you may write that are loaded with GATE at runtime. The license does not affect your rights to this work, only to modifications to core GATE systems.
Basically, you can use GATE Embedded in another system as you like. The only restriction is that if you distribute binaries that incorporate GATE, you must also include copies of GATE, and you must acknowledge your use of our system.