If you go through demo Video of Bizagi you can easily get started with Bizagi in 50-10 minutes.
As I was evaluating it in a way where I have to run processes on exisiting data already in another database. I was searching for functionality keeping in mind that this is a normal case for each and every one except most of information that will be available on forms will be coming for external databases and Bizagi was not an exception.
There is a WIKI on their website that explains how to integrate Bizagi with external datasources which is very good and will help to understand this concept of Replication and Virtualization very well.
have a look at this link and you will definately find it interesting :)
All you need to do is to make sure that your data types are supported by Bizagi. BTW it support most of the commonly used data types you may see details here
In case your table contain columns that are not supported by Bizagi you may use set of supported columns using Schema binded Views with Indexes. For details see my blog for schema binding view
I am not sure but I noticed issues in replication sometime but I will confirm my doubt is that if there is any problem in replicating 1 entity then other entities didnt get replicated