Hi and sorry for late reply,
you can use HTML delimiter field type and Content Plugin to make this, follow these steps:
- Remove Vimeo field from users list page
- Create a custom field of type HTML Delimiter
- Set HTML description in the new field with something like this*:

<a href="/{user vimeo_field_alias displayed raw}"><img src="/url_of_the_play_icon" /></a>

- Edit Vimeo field and add this condition: if equal to custom value (leave empty custom value) then hide HTML delimiter field
- Add the new HTML Delimiter field to be shown in Users List

In Users List you will see the HTML field only when Vimeo field is filled (condition), it will show the Video icon link.

* NOTES:
- HTML editors like TinyMce (built in Joomla editor) should not recognize something like {user ...} as link, so it may change the output, so I recommend you to disable editor when you edit this field.

Docs:
HTML delimiter field type: http://docs.easy-profile.com/index.php/article/html-delimiter-field-type
Content Plugin: http://docs.easy-profile.com/index.php/article/content-plugin