These are difficult because like you say Tealium needs to load and by default we wait until DOM Ready to trigger the server calls to the vendors. However, there are a couple things that can happen:
1) On the redirect pages set all the data needed into a cookie. On the following page Tealium can read that cookie and pass all the data on the next page load
2) Turn the wait flag off for the tag that you need to fire and get your dev team to "slow down" the redirect just enough for the tags to fire. This is difficult because what is "just enough"?
2) **Not a best practice** Code the redirect pages with the synchronous version of the utag.js. With the sync version this will hold up the page until Tealium has loaded. This along with the wait flag turned off the tag *could* fire in time.
Like I said, these are difficult because of the timing issues we face. I would reach out to your Account Manager and have them loop one of us in to look into the nitty gritty of the issue.
There is probably more a challenge to fire pixels on intermediate pages used for redirecting customers. If Tealium is loaded asynchronously on the page. There is a good chance that the library will still be loading when the page is being redirected. There are a lot of factors depending on the type of redirect. Some are:
1. How fast the redirect is happening? Depends on intentional time outs.
2. On the redirect page will Tealium be loaded synchronously? We might be able to fire direct pixels, but library files might not make it.
3. What tags are you firing on this redirect page? If there are external libraries being called those might not run in time.
4. Are your tags cached? If they are cached tags will fire significantly faster, but it doesn't mean it can beat a redirect.