Yes, you can share personal contacts to Secure Folder or vice versa. Go to Secure Folder > Settings > Notification and data > Contact and calendar

1. Import to Secure Folder: Contact and calendar from outside container will be shown inside Secure Folder
2. Export from Secure Folder: Contact or calendar of Secure Folder will be shown outside Secure Folder. (Contact and Calendar app outside Secure Folder)

*Please note, this menu is only available on the devices where Secure Folder is preloaded (e.g. Galaxy S8).