I'd say yes, but only if it's strictly on topic.
In the case of Kickstarter/GoFundMes, the users of this site are going to grill the shill hard, and I mean much harder than the general public would. This can only be a good thing, given the amount of utter horseshit on those sites.
It goes without saying that if the spruiker starts repeatedly posting the same promotional material if met with disinterest it should be considered spam.
I'd also have a higher tolerance for this sort of thing from established members than people who sign up, post their stuff, and fuck off, never to be seen again.
PS: This sort of thing may well be good for new cow discovery too.
Try it. If it doesn't work out you can always reverse your decision.