House Poole is identified as a noble House in ADWD (”The arms of House Poole were a blue plate on white, framed by a grey tressure.”)
As to why Vayon and Jeyne are not so identified, there isn’t a textual explanation, although to be fair they appear very infrequently on the pages of ASOIAF. My “No Prize” explanation is that House Poole is a masterly House in service to Winterfell, and so aren’t lords.
Or it could just be a case of Early Installment Weirdness.