Cloaking is binary. You have cloaking or you don't. Tachyon removes cloaking temporarily, just like when a unit with cloaking fires it loses cloaking. Cloak Boosting only works on other cloaked units and makes their Cloak unbreakable by Tachyon beams. A unit that is cloak boosted cannot cloak boost anything (i.e., no chains). This means scouts form little "packs" of one scout boosting one or more others, and only the scout doing the boosting is vulnerable.
As Scouts increase in mark the number of cloak boosting beams they have goes up. Mark I have one beam, so half of all Scouts are immune to tachyon when they are sent out together. Note however that if enough firepower exists when the scouts pop out of a wormhole and the unprotected scouts get revealed, they can be killed before their cloak boosted brothers get out of range of the tachyon source (normally Tachyon Sentry) which means they too get revealed and possibly wiped out. Thankfully they have Radar Dampening so if they can get far enough out they can still be safe even if their cloak is broken. They just need to avoid getting near anything for the few seconds required to recloak.
But at Mark II they each have two beams. This means scouts end up in packs of 3, with two being immune, so you normally lose only 1/3rd your scouts per wormhole. In addition, Scout IIs are faster so they are less likely to get caught still within tachyon range. Then add the increased ship cap and better radar dampening and Scout IIs are an excellent unlock. Scout IIIs are even more amazing because they get better in every way: cloak boosts, speed, radar dampening, and ship cap.
The Scout Starship has a ton of Cloak Boosting (Mark I has 20!). This means it gets to carry tons of Scouts through wormholes with none of them getting revealed. Its other big advantage is its high health lets it stay alive under fire when its cloak is busted, which keeps it boosting the little scouts around it. So the best way to think of the Scout Starship is as a Scout Escort. It carries its little scouts deep into enemy territory were they can stay and hang out so you have eyes everywhere. The energy cost of the Scout Starship is too high to leave it deep in enemy space though. Try and bring it back once all your fleet scouts are deployed as pickets. I'll let you experiment with Scout Starships and Cloaking Starships and the fun that can be had there.
WARNING: Scouts cost a fair amount of energy. Be aware especially in the early game.
* Some units (Spire Scout and Scout IV) have permanent cloak, which cannot be broken by Tachyon, almost as if they were cloak boosting themselves.