Hi Hannah,
Yes you could do it that way--it would look like this:
*Smart List<Trigger>Campaign is Requested via Marketo Flow Action
<Filter>If filled out form > is > white paper form
<Filter>Was Delivered Email > initial white paper email
*FlowSend Email > Random Sample is 50 - Send Email 1
Default - Send Email 2
Is the white paper going to be accessible to everyone? Or would you like to send a follow up to all those who download it (from site and email) to visit the hub?
If so, you could set it up like this:
*Smart List<Trigger>Fills out form > is > white paper form
*FlowWait > 1 Week
Send Email > Random Sample is 50 - Send Email 1
Default - Send Email 2
Feel free to set the 'wait' time to a couple minutes to test for yourself to make sure everything's running as you like.