Would this be allowed when making a giveaway

Yes but you need to get approval from support first.

i think so

Generally not really on a public giveaway unless specifically approved by support, which I doubt they will do for something as that.

It needs approval from Support, and it can't be a public giveaway, since they don't allow special rules for public or large groups.

thanks

Yup, only by support approval. But I think this rule is nonsense 'cause this isn't real "thank you", but thanks forced by rules, so it isn't worth anything.

yeah what they said but it's a stupid rule

You are no doubt asking because the public giveaways you won in the past you didn't post a useless "Thanks" comment....

what about talking with the winners by steam chat first ? They will probably say thank you then, or by email, its much more personal.

I have that rule in place on all group and private giveaways

So yes

In public and public group giveaways, no it is not allowed.
In private and invite-only group giveaways, it is allowed provided that the creator already had asked for usage and is granted.

Pages of 'thanks!' are a waste of perfectly usable bytes.

It will be allowed for a private giveaway, AFTER consulting with support and approval by support