. . . he seems to force himself upon Aredhel, who bears his child Maeglin, then after Maeglin grows up escapes with him to Gondolin, where Eol follow them, attempts to kill Maeglin, and instead kills Aredhel and is executed himself.

Since it appears that Aredhel was not a willing wife, I would say this is a case of rape resulting in pregnancy and childbirth.

Would the orcs have been able to impregnate Celebrian?  I doubt it.  Indeed I wonder what kind of torment mere orcs could have administered to the daughter of Galadriel and mother of Arwen.  She would have mighty magic indeed, and I think any orc who attempted to force himself upon her would most likely lose his ability to do so ever again.  Either some darker power was involved, such as an orc-chieftan who used to be a Maia, or one of the Nazgul, or even the Balrog, or the orcs tormented her in more conventional ways, which would have presented less danger to themselves.  It was not, after all, THAT hard to persuade an Elf to travel to Valinor.

Here's a UUT for you: perhaps Celebrian was stabbed with a Morgul-knife, like Frodo resisted the effects until her rescue, and like Frodo could not recover from the wound in Middle-earth!  That would certainly explain why Elrond and his household would be familiar with the wound!

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"‘I think he was a silly little man,' said Councillor Tompkins.  ‘Worthless, in fact; no use to Society at all.'

"‘Oh, I don't know,' said Atkins, who was nobody of importance, just a schoolmaster.  ‘I am not so sure: it depends on what you mean by use .'

"‘No practical or economic use,' said Tompkins.  . . .

. . .

"‘It is proving very useful indeed,' said the Second Voice.  ‘As a holiday, and a refreshment.  It is splendid for convalescence; and not only for that, for many it is the best introduction to the Mountains.  It works wonders in some cases.  I am sending more and more there.  They seldom have to come back.'"