I've been doing geospatial development since 1992 when Genasys (defunct) released the worlds first web mapping server, Web Broker (ESRI's IMS wasn't released until 5 years later). At the time the only COTS option for managing spatial data within an RDBMS was Sybase's Spatial Query Server, which provided slightly more geometry options inherent within MySQL today. MySQL geometry features should be considered primitive at best, far from a full-featured implementation. On the other hand, PostGIS, is full featured and the only open source implementation I know of that adheres to the Open Geospatial Consortium's 'Simple Features: Types and Functions 1.1' specification. It is very robust, scales well (in contrast to MS SQL) and you can't beat the price or ease-of-mind that comes with being licensed under v.2 of the GPL. Additionally, on comparable hardware, in terms of reliability, performance, and cost effectiveness, there is no comparison, regardless whether your using Oracle w/Spatial or MS SQL and ESRI's SDE.
Your developers, as good of guys at heart as they may be, should stay away from the kool aid for awhile