Can ...

RewriteCond %{REQUEST_URI} ^/folder1/ [OR]
RewriteCond %{REQUEST_URI} ^/folder2/ [OR]
RewriteCond %{REQUEST_URI} ^/folder3/
RewriteRule (.*) / [R=301,L]

... be rewritten to ...

RewriteCond %{REQUEST_URI} ^/(folder1|folder2|folder3)/
RewriteRule (.*) / [R=301,L]

?

And when so, could they be absolutey identical in functionality?
Suggestions/enhancements tend to be appreciated.

Those are the same factor, the | means OR therefore if it begins with /folder1/ or /folder2/ or /folder3/ perform the redirect.

So yes it might be shorter and exercise to your requirements.

As Pekalski recommended you may make it shorter with:

^/folder[1-3]/

A couple of more good examples and references are available at: http://semlabs.co.uk/journal/mod_rewrite-quick-reference-and-cheat-sheet