That's pretty much what I do for preview.
One reason for failure that I can think of, is that the control cannot enumerate devices (i.e. oleVidCap.getViewDeviceCount()...).
Update: I see that you mention that using .Object fixed it. For me, it works ok with a direct ref (no .object)

>>I use VideoCapX. Simple to use and reliable in my tests so far. Have not used it in production yet.I believe they have a trial version, as well.
>>http://www.fathsoft.com/videocapx.html?gclid=CJbjzaSTzKUCFdJL5QodFmepnQ
>>
>
>Thanks for the link. I'm trying out their control but when I try to preview, it fails.
>
>thisform.oleVidCap.videodeviceindex=0
>thisform.oleVidCap.connected=.T.
>thisform.oleVidCap.preview=.T.
>
>
>You doing anything more than that to make preview work?