I'm in the middle of reading Helen Nicholson's "The Knights Hospitaller," and discovered that CB may have had a good historical basis for giving Hospitallers frenzy. Apparently, historical records indicate that in several major battles in 1191-1192, against Saladin, the Hospitallers were rebuked for charging too early into battle. That got me to wondering, what other troop profile attributes in military orders have associated historical events that could be seen as inspiring CB in their design decisions?
Templars get a 'but of course' note, as many of them were found not guilty of technoheresy (ie, researching AI). Gabe De Fersen is simply the posterboy example.
Santiagos had a seafaring tradition, as well as one of protecting pilgrim routes. Making them space marines of Infinity is quite fitting.
IIRC, there's a sub-order of Hospitalliers, the Order of St Lazarus, who are taking care of the sepsitorized. The historical Order of St Lazarus ran hospitals in the Holy Land caring for lepers.
Teutonic Knights were dispatched to the outskirts of the christian Europe to 'fight and convert pagans'. In Infinity, their monastery is located on the Paradiso (one of newer planets under influence of HS) where direct conflict with CA takes place. #3rdOffensive :P
The Order of Montesa was basically a serial-numbers-filed-off replacement for the Templars in the Crown of Aragon because the Templars had been so popular there, so them being brought in functionally as a local stand-in for the Hospitallers in Aconticimento seems very appropriate.
At the Great Siege of Malta in 1565, in which the Hospitallers held the island against the might of the Sulieman the Magnificent's Ottoman Empire, the defenders of the doomed Fort St Elmo wrote a letter to the Grand Master saying that the conditions were so miserable they wanted only to charge out and die like knights. They had to be shamed into holding their defensive position for as long as possible, which they did for another fortnight. (Heartily recommend reading 'Malta 1565 - the Great Siege' by Ernle Bradford - its brilliant stuff, very readable!) I've not read much about the Order of Santiago, but I think in the late medieval period, and (especially) the 16th Century when the battle for Mediterranean between the Ottoman Empire and Christian Europe reached its height, the Hospitallers were the most significant sea-faring military order. Their 'piracy' of Ottoman shipping was so disruptive (thanks in part to their strategic position on Malta) that it forced the hand of the Sultan to embark on the Great Siege.