How did ODBC came into your solution? Do you use a ESS to FileMaker Cloud to reach your ODBC data?
From FM Cloud you can reach your solution from any network, that is the basic idea of the Cloud.
FileMaker Go and FileMaker Pro works on same port and you do not need to change any ports from your iPad/iPhone to be able to reach your solution
I am developing an application with FM GO using the filemaker cloud. I have an external database hosted by the same site
This may cause some confusion. Are you talking about 'FileMaker Cloud' the product? Or just that you have FM database hosted somewhere in the cloud? 'FileMaker Cloud' as a product does not have the capability to host a non-FM database.
Or do you mean 'external database' to be another FM file referenced by the first file? If so then ODBC wouldn't come into play at all.