We’re very careful with how we use the word “support” here - ManageIQ is not commercially supported in any way. However, it is open source, and you can get help from the community for pretty much anything. The best way is to try to figure out how to do it yourself, and ask when you have problems.
To be specific, when you talk about the “Dialogs” section, are you talking about the Provisioning & DService dialogs sections under “Automate->Customization”? There is a blog entry by John Hardy on creating custom dialogs there with a code snippet which you can use to pre-populate drop-downs - I’m not sure if that’s exactly what you’re looking for. Hiding a field in a dialog is described in the CloudForms docs.
I’m not sure if this helps - perhaps you could give a more detailed description of what you want to accomplish?