actually, there are a variety of jewish relics, mostly broken pots and the such, in the eastern region and sinai. It's not a huge amount, but it's there. The significance is debated, as jews weren't somehow less mobile than every other group. And it's not the only time the jews were under the rule of the Egyptians, as Egypt ruled over Israel later on.
As for Egyptians covering up stuff, look at the Amarna Period. Tutankhamen actually did a spectacular job covering up all evidence of the period, leaving it well buried for thousands of years. And that's actually the people that were considered important, rather than some slaves. Do keep in mind that we didn't start excavating the worker quarters around the Sphinx until fairly recently, showing our own priorities.
And I don't know if I would say this is a 'conspiracy', as that usually suggests a story differing from the accepted truth during or after the fact. Egyptology is younger than the bible, so in a way the archaeology is pushing against the accepted truth of the bible. Although there are certain aspects of the bible that are rooted in history, there are also parts that were exaggerated. There is proof that a famine hit Israel shortly before the supposed slavery in Egypt and the Israelites were known to move to better regions. Just as Jesus was ignored by the authorities of his time (the Caesar knew nothing of the man), the Israelites might have been run of the mill slaves who managed to escape (of which the Egyptians would have cared little) and they just blew the story out of proportion. Wouldn't be the first time a culture did that.
