When playing Support of the Eagles from the top of your deck using hero gandalf's ability, can it be attached to him, since he is considered to have the tactics icon while playing it?

Yep!

1 hour ago, Bobbymcbobface said:

When playing Support of the Eagles from the top of your deck using hero gandalf's ability, can it be attached to him, since he is considered to have the tactics icon while playing it?

Correct, also Burning Brand and other attachments with sphere limitations.