Using Views DataSource and Feeds to pull content from one site to another... with multiple images
Disclaimer: This is a should-be-deprecated approach, both Views DataSource and Feeds can be replaced with better options, such as Services or RestWS to Rules and Rules XPath Parser. But this approach basically works now.
On the source site.
Making Views Datasource Output multiple values for an image
drush dl image_url_formatter
drush -y en image_url_formatter
Configure the View to use it for the desired image field ("Image URL" instead of "Image").
Seems to be an arbitrary hard-coded limit on 8 values in Views Datasource.
Making Feeds accept a multiple value field
drush dl feeds_tamper
drush -y en feeds_tamper feeds_tamper_ui
xpathparser:7 -> Your Field with Multiple Images
Leave at default setting of comma.