The Defined Limits
SharePoint has a stated content database size limit of 200 GB or 4TB (if required disk sub-system performance can be achieved).
This limit is described as a 'Supported' limit by Microsoft which means "Configurable limits that have been set by default to a tested value". This is the lowest of the three different types of limits set by MS, the others being Thresholds - "Configurable limits that can be exceeded to accommodate specific requirements" - and Boundaries – "Static limits that cannot be exceeded by design".
To further illustrate Microsoft's stance on Supported limits – "It is important to be aware that many of the limit values that are provided in this document represent a point in a curve that describes an increasing resource load and concomitant decrease in performance as the value increases. Therefore, exceeding certain limits, such as the number of site collections per web application, may only result in a fractional decrease in farm performance." Although they do then note that exceeding such limits "is not a best practice".
How does this affect RBS?
Microsoft state within their discussion on the 200GB limit that "If you are using Remote BLOB Storage (RBS), the total volume of remote BLOB storage and metadata in the content database must not exceed this limit." Given that RBS improves overall SharePoint performance and reduces load on the content database's disk sub-system it would seem to be merely a documentation oversight that RBS is not mentioned in the supported limit of 4TB.
Microsoft state that "thresholds and supported limits guidelines are determined by performance", but in the case of RBS they do not test with third party providers such as Stealth Content Store for SharePoint (SCSS). They acknowledge the increase in performance and reduction in SQL load, they state that RBS is of optimal use in situations where (amongst other things) "The resources on the computer that is running SQL Server might become a performance bottleneck" [technet].
This leads to an interesting outcome. Microsoft has defined a Supported limit that is based on internal performance testing. In the case of RBS this is without access to the actual software used to implement this feature.
By their own acknowledgment the Supported limits may be exceeded based on specific requirements and result in minimal performance degradation. In the case of SCSS you are already getting a performance increase that exceeds the baseline.
If operational requirements create a need for exceeding the 200GB limit then that is the overriding business requirement. A Supported limit will not prevent that, the performance should be monitored and certainly an RBS provider such as Stealth Content Store for SharePoint will help mitigate any problems with SharePoint's performance.
All quoted sections are taken from http://technet.microsoft.com/en-us/library/cc262787.aspx unless otherwise stated.