Well I am not too sure but fecal matter can infect you. Say you dip your finger in and then play with yourself and then dip in for more lubrication: You just transferred fecal matter into the container of vaseline. If someone goes and uses it on their feet or skin, they probably wont be infected. But say someone puts some on their chapped lips. Fecal matter could be ingested. I am not sure if this is even possible or about the science of it all. But I personally would not do that to a unsuspecting victim. Wouldnt you be grossed out if it happened to you?
You can still use it just put clean hands in there and dont double dip. Keep things very sanitary. Its good to be clean when doing anything with the anus.