Is "Laudatio omnibus Dei" grammatically correct?
Yes. Without more context, it is grammatically correct.
It would mean "praise for God [is] for all" (obj. gen.) or "God's praise [is] for all." (subj. gen.). It could even carry an implicit sense of responsibility, like "praise for God [is an obligation] for all."
I want, however, to question the use of laudatio instead of laus, laudis. Laus is the go-to Classical word for "commendation, glory, fame, renown, esteem," and even "praiseworthy things/deeds." Laus, laudis lexicon entry
Laudatio on the other hand is it's more abstract cousin. Laudatio means "praise" as a completed action, like "a praising." It lends itself, therefore, to meaning "a eulogy," "a panegyric," or even "favorable character testimony" in court. Laudatio lexicon entry
So unless you're talking about a specific prayer, you may want to consider changing laudatio to laus.