There are no known issues with PagSeguro. Because many gateways are cross border, I'm not sure if there are any others specifically for Brazil, but we may be creating one or more new gateways for Brazil soon including Widepay.
I'm not familiar with boleto bancario. You can see a list of gateways at https://docs.blesta.com/display/user/Gateways
If a customer does not pay, their services they have with you can be suspended, but it does not currently have any impact on whether the client can open tickets. Your support staff can check the status of their account, and ask them to bring it current in order to provide support. Or, a customization could be made to disable it if they are behind.