Yes, it will be safe to plant them out in the ground..
dig their new holes 1 1/2 to 2 x as big as the pot they are in. If the soil if poor quality [like mine] mix in some compost with the soil. Plant them to the same depth they are in their pots and back fill with the soil/compost mixture. water well and make sure they don't dry out for at least a month.

Just out of curiosity which Hydrangea is it? Usually the majority of hydrangeas don't need much pruning, you only remove the faded flower heads and leave the rest of the stems intact.

Have not a clue I got 2 from dobbies just before lock down from the reduced isle 1 didn't make it I didn't have to prune it as the frost got it and the stems ended up mush I just cut down to the hard stem it did produce lilac and purple blooms last year if that's any help?