Yes he can. It is a valid concern. All I can say is that what I know comes from the Holy Spirit. Sorry if that isn't a very satisfactory answer, but it's all I've got on that one.
Coincidentally, in the Doctrine and Covenants (a part of the LDS cannon) it describes how to tell the difference between an actual angel and a demon masquerading as an angel:
http://scriptures.lds.org/en/dc/129/
Sorry, but I can't seem to figure out what you mean here. I think you forgot part of the refference
There probably is an LDS church not too far away though. Go to
www.mormon.org and click on the "Worship with us" link at the top.
There are some good apologetics sites too, but remember, these do not represent the church. They may answer some of your questions though:
http://www.jefflindsay.com/LDS_Intro.shtml
http://www.fairlds.org/