集体户口上一页有许多名字，是否需要作什么标记指明我的名字给移民官看？

Don't worry, I think the visa officer knows Chinese. :)

Seal 是否盖在我的名字上？

It should be. But not very important, I think.

最后，是否可用这个证明办理出生公证等？

You may try it. If the notary doesnot agree, maybe still you have to try another way. The rule in China is no rule. :(