You're right. In informal conversation, いる sometimes means 'to need' as well as 'to exist'. But when you want to use it in the former way, and when the sentence object is a creature, you need the context suitable to the usage. Otherwise, we will definitely misunderstand what you are getting at. 道具/どうぐ/がいる; we need tools. // it won't be misunderstood because いる is only used for creatures. イヌがいる: without context, we think you want to say 'there is a dog'. このシーンを撮影するためには、イヌがいる: To shoot the scene, we need a dog. Also, the usage requires right nouns for sounding correct. if you want to go safe, you'd better refrain from the use when to speak, I think.

いぬがいる -> there's a dog いぬをかっている　-> I have a dog