In short, no.Â

Best case scenario for the Strahd zombie, let's assume hard to kill would be equivalent to incorporeal in that it would generate hitpoints x2 and furthermore assume the presence of the grim necromancer cfx for the Strahd Zombie. Then effective stats in summary would be:

Strahd Zombie LE
20 points
AC 16
HP 80
Melee Attack +10 (10)

Sacred Watcher LG
18 points
AC 21
HP 60
Melee Attack: +10 (10)

Under these assumptions the Strahd Zombie might be comparable to the Sacred Watcher against the average target. Of course, Evil Undead slayer would still allow the Sacred Watcher to cut the Strahd Zombie into tiny zombified pieces. To make up for this we might also assume that "plodding" is a good ability which would allow the Strahd Zombie to, say charge with the power of a runaway train wreck, pushing back all units of equal or smaller size the charge hits, allowing it to continue its charge until it misses an attack. Perhaps then the Sacred Watcher and Strahd Zombie would be of comparable worth.

Problem is these best case assumptions would seem chancy at best. Considering what other posters has written here, more likely "hard to kill" is inferior to incorporeal. Furthermore the presence of a Grim Necromancer can hardly be relied upon and likely plodding is an ability which weakens the Strahd Zombie. I'd expect "hard to kill" to generate perhaps 10 hp on average, presuming it will deflect a killing blow for 20 damage 50% of the time, meaning the Strahd Zombie would have equivalent to 50 hp. Then a comparison would look something like this:

Strahd Zombie LE
20 points
AC 16
HP 50
Melee Attack +6 (10)

Sacred Watcher LG
18 points
AC 21
HP 60
Melee Attack: +10 (10)

The Sacred Watcher would in this case seem to easily dismiss the Strahd Zombie in head to head combat relying on its base stats only. (With the Sacred Watcher's Evil Undead Slayer there would be no contest at all.) So no, the Strahd Zombie would not seem comparable to the Sacred Watcher in any way. Rather the Strahd Zombie would seem fairly close on the power curve to recent, similarily costed undead such as the Terror Wight or the Skeletal Reaper. Pieces which one would be inclined to characterize as fairly mediocre. 

i think that we are comparing the wrong things here.

shouldnt we be asking, is a strahd zombie as good as a skeletal reaper?

now, thats a much better debate, since everyone who can read can tell the sacred watcher is much much better than either of t hem

both lvl 6 spd 6 (plodding) vs spd F6 ac 16 vs 17 both 40 HPs AB +6 vs +7 each 10 damage strahd zombie has hard to kill vs skeletal reapers devastating attack, seem pretty equal, both pretty weak when you can find cheaper figures with better attacks