Are the shivalingam and the orphic egg possibly a similar thing being represented differently because of cultural emanation?
Yeah, there is great similarity between the two.
Orphic Egg - Wikipedia
The Shivalingam in Hinduism is also considered the cosmic egg from which sprang forth everything in the material universe, including the gods, at the time of creation, and they will all return back to the Shivalingam at the time of cosmic dissolution.
The orphic egg is considered to be the creator of all the other gods.
The Prajapita Brahmakumaris consider the Shivalingam as
a point of light, to be the father of all the other gods and sentient beings.
Like the Orphic Egg, the Shivalingam is often depicted with a serpent wound about it.
The devas (gods) in Hinduism also mean 'Shining one's' similar to the gods in the greek tradition who are considered luminous.
It is possible that there is a common link and origin to these traditions.