If a dental implant that has temporary cement cannot be removed for permanent cement, can this result in bacteria to collect and cause decay?

Implant crown: It's the implant crown that has the cement, not the implant. Implants & crowns are made of titanium, gold, and porcelain, which do not decay. Keep the area clean and you should be fine until the prosthesis loosens up.

Not a problem: There is no tooth structure to decay so the simple awser is no. Many dentists actually prefer temporary cements as it can (usually) make removal of the implant crown easier for maintenance and the like.