Canon Law does not address the issue of parish priests hearing the confessions of their employees. However there are some cases where canon law recognizes that hearing confessions can cause a uncomfortable conflict of interest:
Can. 630 §4. Superiors are not to hear the confessions of subjects unless the members request it on their own initiative.
§5. Members are to approach superiors with trust, to whom they can freely and on their own initiative open their minds. Superiors, however, are forbidden to induce the members in any way to make a manifestation of conscience to them.
Can. 985 The director of novices and his associate and the rector of a seminary or other institute of education are not to hear the sacramental confessions of their students residing in the same house unless the students freely request it in particular cases.
In seminaries and religious life, those who have authority over others are cautioned against hearing the confessions of their subordinates. The reason is that this situation creates an untenable tension between making objective and public decisions while at the same time knowing personal information that cannot be legitimately acted upon.
As previous stated, canon law does not address parish priests and their employees but the general principle of “conflict of interest” could arise and it is generally not a good idea, IMHO, for parish employees to confess regularly to their boss. Whether or not there is actually a diocesan rule stipulating that I cannot answer, you would have to consult the particular diocese.
I know of one situation where it was discovered that a parish money counter was stealing money from the parish. The individual realized that the pastor had found out and quickly tried to “poison the well” by going to confession to the priest. He, fortunately, knew what was happening and wisely refused to hear the confession. But had he not known he would have been in an awkward situation of parsing what he learned outside the confessional from what he learned inside the confessional.