Ministeriales are quite the subject of contention in high medieval German setting, their origins oft disputed, and regional differences noticable, and further some differences between ecclesiastical, imperial, and other noble ministeriales. Although it is a bit unclear what are you asking about? Are they a significant and indeed very important phenomena between 1000-1300 in Holy Roman Empire, the answer is uncententiously of course, they were primary force of both Salian and Staufean Dynasty, and by the late thirteenth, specially fourteenth, with multiple grants of privileges, both imperial and local, their statues goes through significant legal and social changes, so by the end of medieval period, the differences between "old nobles" and those descended by ministeriales have different functions, and solidly occupy the lower Nobility.

As wikipedia quotes;

The ministeriales (singular: ministerialis) were a class of people raised up from serfdom.

Well, this is disputable, and, for example^(1), Arnolds´ pushes significantly against this as a general origin, probably best established A.F. von Furth and G. Waitz in nineteenth century, but this in turn was heavily pushed against by late nineteenth and early twentieth century historiography ( such as W. Wittich, G. Caro, P. Heck. V. Ernst, etc. although with substantial differences between them ) as it would concede that plenty of most powerful German noble families had servile origins, so it was partially a response in scholarship to nationalistic pressures. So, in post-war scholarship, this dies out, but there is still no single consensus about the nature of origin of German ministeriales.

In terms of marriage, plenty of important documents ( notably, for the ministeriales of Cologne ) that they could marry within the set of ministeriales of Cologne, but not outside it. We have documents for Bamberg ministeriales from 1125 threathening disinheritance if they married outside their class and lordship, and other hereditary and jurisdictional privileges.

Now, since it is hard to talk generally about a whole "class" across such a timespan, so on this note, I would be thrilled to be met with a more narrow and slightly more precise-inquiring question as to be of use. As for why this phenomena is not widely known or talked about, who knows. Partially, it is quite German-specific ( or HRE ), so outside of German discourse it is scarcely found, and secondly, medieval history, beside the usual popular notions, is not all that much of interest generally.

I am not familiar enough with either Janissary or Mamluk classes to offer any meaningful comparative analysis.

1. I can say the most complete work on the subject is Arnold´s German Knighthood, 1050-1300, but it has its points of contention ( or rather, some things are not settled upon ), and some issues which would warrant closer inspection are rather left unnoticed, but all these are minor reservations with a magnificent work.