Pinot Gris is more commonly called Malvoisie here. What little there is planted is often used to make a late harvest wine – sweet or semi-sweet depending on the vintage and the style wanted. It is rare to find it on sale. Instead an unlabelled bottle for personal consumption is more common. Further west in the Coteaux de l'Ancenis Malvoisie is relatively common. It is one of the three Pinots used to make Noble Joué (or rosé or vin gris) – the other two are Pinot Noir and Pinot Meunier.
Menu Pineau (also called Arbois) is a relation of Chenin Blanc. Once relatively widely planted it lost a lot of ground after the arrival phylloxera and during the 20th century. It can make attractively minerally dry whites. Some producers, like Pascal Potaire, are making 100% versions and I hope this coming decade will see more examples being made. Along with Chenin Blanc, it is the other grape of Vouvray, although this tends to be downplayed.
The official decrét (text) for the Vouvray appellation is unequivocal:
'Art. 2. - Les vins ayant droit à l'appellation contrôlée " Vouvray " devront obligatoirement provenir des cépages suivants : gros pineau ou pineau de la Loire ou chenin et petit pinot ou menu pinot.'
Interloire's site is an example of Menu Pineau being downplayed as Chenin Blanc is given as the sole permitted variety for Vouvray.
It would appear here that 'pinot' and 'pineau' are interchangeable. The rules appear to allow a Vouvray to be made from 100% Menu Pinot or Pineau. I have no idea if there are any examples of Vouvrays made from 100% Menu Pineau – if anyone knows of any I'd love to know please. In contrast to Vouvray, Montlouis allows only Chenin Blanc.