After reading the agreement on the link you posted, it appears to me that it was an agreement with the PA. Since Hamas, not the PA, is in power in Gaza, it would seem that the agreement is moot. Therefore Egypt WOULD be in violation of their treaty with Israel if Egypt were to open that crossing on their own.
Israeli troops shoot, injure Palestinian crossing Gaza border fence (Haaretz)
from the article: Israel: Gaza crossing to stay shut as long as Hamas in power