If you are sure that the client is for real, I would go ahead. However, let them know that you can video chat now through Upwork. Some clients want to Skype to verify your language ability or for other reasons. I don't typically provide my Skype until I have a contract that shows in My Jobs tab.
I'm unconvinced it does not affect your account. That's news to me, because whenever I respond to a potential client who wants to interview me, and I let them know that I usually do not use anything outside of Upwork until after I have a contract and NDA etc. in place with them, Upwork will highlight terms like "Skype" in yellow and I'll receive a note on the page from Upwork saying that it's against service terms to communicate with a client outside the platform. If it's okay to provide a skype ID to a prospective client why does Upwork flag the names of software and the phrase "e-mail" etc. throughout our messages?
Separately, I have to say I'm really aggravated lately by just how many prospective clients are requesting I interview or work with them off of upwork. It basically means I am using up all these credits that I now have to buy instead of having a certain amount provided free which are WASTED because prospective clients have a complete lack of integrity. So, Upwork isn't properly vetting these clients before they get to post these huge contracts that lie and say they're looking for "6 months at 30+ hours a week," which is the kind of client I normally prefer working with both here and off of Upwork. So, I take time to craft a proper proposal and provide work samples to the spec of their job listing (making the assumption that they are a legitimate prospect), and then they come back with requesting that I interview with them off of Upwork. When I say I don't do that they try to get me to call their phone outside Upwork and refuse to set a proper interview time and try to get me to call or skype. This happens for approximately 70% of the jobs I answer. This is horse manure. Upwork, either properly check and filter the paying clients you are letting onto your platform, or REMOVE all your threats against contractors that your unvetted clients keep creating themselves by putting them in a bad position. Basically, not only is Upwork putting Upworkers like me in this bogus position, the prospective clients are, too, which again, Upwork is responsible for vetting. How nuts is this? Why would anyone want to work this way unless they were starving to death? (And therein lies the crux of your whole platform success, right?) You get lots and lots of Upworkers who don't care and will do anything including breaking the rules for $5, because they don't think they have any other choice. This is not unlike indentured servitude for people in 3rd world economies. For the rest of us, it's just unethical, a bad business model, and perhaps could be addressed, but hey we've got a president breaking the law every day, so why should anyone else follow the law right? If you don't have to properly screen prospective clients who break the law, why would you expect Upworkers to follow your terms and conditions?
w/a Roxy Rogers
Washington DC ~ Berlin Germany