Even IF i wasn't in a position of knowledge about Riots MMR detection system, it would be quite natural that VPN would indeed not protect you, or your customers.
Heres a rant about services that adv. VPN AFAIK there are 4 types of services.
1. The service that advertises safety through VPN (does not use it) and takes a fee from it.
2. The service that believes in good will that the VPN will protect them and their customers and does not charge for it.
3. Then there are the services who believes it keeps them and their customers safe but also charges for the VPN useage (very douchey IMO to charge ur customer for VPN when the safety is a 2 way road. In this service owners mind it's okay to charge your customer for a VPN service to keep his own account safe) The key thing about this is, this booster/service would of used the VPN service in any case had the customer not paid the fee, just in order (according to his knowledge) keep his main safe.
4. Then there is the services that dont provide VPN, do state that, but also do explain why it wouldnt help even if we used it. Which i am a part of.
Take it as truth, or a grain of salt, only been in the business for 5 years and only know of 1-2 whose been banned either outside my service, or customer who didnt adhere to the rules of the boost. If you are a really really good booster there are ways to not get banned, if done poorly, or irresponsibly however, it will be happen (or just lack of knowledge really which isnt ones fault persay, this is not bashing towards u in any way.)
Although buying botted accounts is detectable in many cases, and has a high banrate. i would stay away from that. only way to keep urself semi-safe is looking for services who actively advertise with banguarantee and even then they regularly get banned after a month or 2 or 3. (note some smurf services actually only hold their warranty valid for a month or couple weeks after purchase... laughable)