Not sure, I would not recommend trying to find out though as they might. If you do I would suggest create a fake dummy account to do so. The downfall in my eyes is spamming looks bad for the user + the site in reference. However using the PM method I do not see how they would tell you were spamming (like if you were doing it in the comment sections).
Any site can ban you. Spamming members is one of the quickest ways to get banned. If they associate you with your Google webmaster account, adsense, adwords, Google Talk, G-mail, Analytics, and the websites that you own and deem you a spammer, you will be in for a world of hurt. Spam don't pay.
I don't know - I doubt it if it's legitimate. I've been on the receiving end of mass PMs from one guy for almost two years now. But even with that said, I don't know if I'd risk it.
Anything unsolicited is usually considered SPAM. If it is an opt in list or sign up, then they have given permission to inform them of new offers and such. Most platforms allow you to message members and most people understand that by joining a group that they will get updates on group activities and information like new blog posts and such, but, constant solicitation within a group on a social site like You Tube can be considered SPAM as well and if you are reported it could lead to them taking action against you for violating what ever their T.O.S. is. Personally, I just drop my affiliation with the group so that I can't be messaged anymore. No one like to be constantly solicited to buy something no matter what platform or situation it is.
I see. But I'm thinking of just letting people know about the site, and if they interested, they can reply with an email address. Otherwise, I won't bother them anymore.
If you send it to a few people only, than YouTube will leave you alone. However, if you send 100 PMs that are the same, they will suspend your account. The problem is, for your marketing to be successful, you need to send 100s of messages, so yes, it will get you banned. This is true for other websites as well, not just YouTube.
Yes, if enough people report you, sure you can get banned. Why would you even think of sending hundreds of messages anyway? Why not make some interesting videos, post them on youtube and use the site the way it was intended. There is no reason to spam. In the amount of time you can send some private messages, I can make a good video, post it and be getting thousands of views.
I posted 3 videos already related to my niche and only got a dozen or so views so far. You will only get thousands of views if your video is about making quick money online or teenagers doing stupid things. 70,000 videos are posted each day on YouTube, so your video really has to stand out from the rest of the crowd or you will not succeed marketing your website this way.