There were several titled Jewish British families by 1912 (several more have been ennobled since). The Montagus, for example (original family name was Samuel). Venetia Stanley - Clementine Churchill's cousin and close friend - converted to Judaism and married into this family. The Rothschilds had also long since been titled by this point.
I know that the Lusitania's Gladys Crompton's father was in the military. His family, the Salis-Schwabes, was of Jewish origins but I believe had converted to Unitarianism before he was born.
Also, the Lusitania's Goldiana Morrell was Jewish and had a son in the Queen's Own Rifles.
But I don't believe that the Morrell family's name was originally Morrell, and it is telling that Edith Rosenbaum, the Christie family and the Lusitania's Anne Shymer (Shimer, in reality) felt the need to anglicize their names.
I think the issue is one that there isn't a lot of rhyme or reason to. Jews were widely accepted socially and otherwise on both sides of the Atlantic and also experienced varying forms of discrimination on both sides of the Atlantic. I think that whether one's origins - religious, ethnic, socioeconomic - helped or hindered one depended on how one "carried it off".
On the Titanic, there were several interdenominational marriages - the Rothschilds, Dodges and Cavendishes (and maybe Stengels - she was Christian; don't know what religion he was).
According to Dorthy Parker's bio (nee Rothschild; niece of Titanic's Martin), Martin's family actually encouraged their sons to marry Christian women for the sake of gaining more of a foothold in mainstream USA.
But the same book also said Elizabeth Rothschild was the heiress to the "Great Bear Springs Water Company", when I believe her origins were actually quite humble and she wasn't an heiress of any kind. So who knows.
The same thing was true of Catholics on both sides of the Atlantic. We always hear that they were excluded from high society, but in the States, the Iselins and Carrolls (both New York 400 families), along with most branches of the Drexels and several branches of the Vanderbilts were Catholic. In Ireland, the Earls of Fingall and Granard, and the Viscounts Kenmare and Gormanston were Catholic. Elsewhere in Britain, the Dukes of Norfolk, the Marquesses of Bute, the Earls of Abingdon, and the Barons Petre, Stafford, Llanover, Lovat, Clifford, and Stourton were Catholic. So were a lot of ancient, highly-honored families like the Blounts, Blennerhassets, Welds, Fitzherberts, Throckmortons, Actons, Sulyardes, Mostyns, de Traffords and numerous others.