Copyright

Files you find on those sites, Vecteezy, freepik are everywhere.  Be very careful where you spend your money. So many of these sites even if they are selling materials do NOT own the rights to those photos.  Take any of the free vectors you have downloaded, now load it into Google Images and watch jsut how many other websites have that same file.  Many of these "pro" version of files one one site that you have to pay $$ for, are free on another site.  It's a really muddy sitution, you could go and pay for a file, and find out you are still not allowed using it.  These sites are now a dime a dozen, and are popping up all the time.  Many of these sites are bogus too, even though they are asking for money for a specific file, so you really do need to do your homework. The bottom line - if you are going to be using that vector for professional work, you had better contact the owner ( the real owner ) of that vector and get proper documentation.  I find it funny, you'll see so many huge accounts on Instagram, Facebook for example, - News stations, radio stations, stealing artwork, and not even trying to hide the fact they did ( the watermark is still on the photo ) and using it without any concern.  Nobdoy calls them out for this, it's unbelieveable.  Imagine a huge news agency using that on their FB pages, their Instagram etc..... to annouce a contest, etc or whatever they are promoting. It's shameful. 

Copyright gets very sticky when you use any part of someone else's work in any project you get paid for or sell. The long and short of it is, if you do not have a signed release to use copyrighted materials in your copyrighted and sold project, no matter what kind of project that is, you are opening yourself to the possibility of a lawsuit, and damages could be substantial. No copyright agreement or license in your hand with specific clearance for including the material in your paid work or paid-for product could be as dangerous as handing a four-year-old a loaded gun. You might get away with it a few times, but eventually, somebody is going to get hurt. 

If you are serious about selling your creative work, read this book: The Copyright Zone. I have a copy and have read it three times. Almost all of my original work is copyrighted, and the licenses are very specific. 

If your work is not for profit like the amazing series "OwlKitty", you can get away with a lot. YouTube publishes the content but cannot and will not pay him a dime even though he has 2.3 Million subscribers. On the other hand, he has a perfectly legal website where he can sell OwlKitty merchandise or become a patron. OwlKitty is a good example because his amazing videos are created using After Effects and MOCHA.

The long and short answer is: Maybe. Such questions cannot be answered with a simple yes or no. It depends on the licensing terms of the vector artwork and on the other end on what the stock site will accept. And then of course there's the question of where you live and how the stock video could be used. What's allowed in one country could be restricted or prohibited in another. Also there are differences between free content and commercially sold items. That being the case, the only reliable way to know is to intensely check the licensing FAQs of the artwork provider and the site you plan on uploading your videos. Everything else would just be an endless guessing game.

Mylenium 

Check the icense agreement provided by the free vector graphics site.

For example, Vecteezy requires attribution unless subscribing to single license only (one user only) plan.  So, we can download and use the graphics in our motion design but may have to provide attribution.  This is their Licensing Chart for more details and this is the full License Agreement.

If you're still have questions or concerns, schedule a consulation with an attorney who practcies copyright law.