No, Siamese cats are not less allergenic or hypoallergenic. Siamese cats are like any other domestic cat. They produce the allergen in their saliva which is deposited on their fur and which results in dander flying around the room containing the Fel D1 allergen which makes allergic people react in various ways from itchiness to runny eyes et cetera.

This cat allergen is not dependent on the cat being purebred or random bred despite what the internet might tell you.
There are tales of Siberian cats being hypoallergenic. Not true. Breeders like to promote their cats.

The so called hypoallergenic cats – Allerca cats – are not hypoallergenic, except the top of the range Allerca cat the Ashera GD is a Savannah F1 and these cats seem to cause less of an allergic reaction in people but we don’t have firm evidence of that.
Some people might say that their Siamese cat does not cause an allergic reaction whereas other cats do. That may be true and it may be because the individual cat rather than the breed is hypoallergenic. Or the person has got used the allergen and become desensitised.
Nothing more to say really. Do you disagree? If so please tell me why.
Conclusion: Siamese cats are not less allergenic. Link: Fel D1 — Ways to combat a cat allergy — allergy may fade.