There is no evidence of the Welsh wearing a sporran. The Welsh used to wear a leather wallet called a 'sgrepan'. A 'sgrepan' is a very important part of the regalia serving to decorate and protect the wearer. It is made from leather, Welsh goat hair, Welsh cob hair and has leather straps.
One thing to keep in mind here is that sporran is simply the Gaelic word for a pouch. So to say that the Welsh did not wear sporrans is like saying they didn't wear pouches. Which only leads one to ask, "Where did they keep their stuff?"
And what of this "Sgrepan" that they are talking about? Well, I don't speak Welsh, but I would suspect that this is simply the Welsh word for a pouch or purse. If you look on their product pages you will find a listing for an Ysgrepan (one has to assume the same item is meant, though I don't know the reason for the different spelling). And what is it? Well, it looks an awful lot like a Scottish sporran... no surprise there.
The verdict. I have nothing against non-Scots, be they Welsh or Irish or Austrian or Iranian, wearing tartans and the kilt. I am flattered that they think highly enough of the Scottish national dress to want to adopt it. And if people want to design new tartans specifically for non-Scottish groups and families, go for it. But please, please, do not debase yourself and insult the intelligence of others by making false historic claims for these new designs.