You can have an Other Pay Type Pay or a Regular Pay Type Pay retrieve a rate of pay from a Pay Rate Table.

You can either setup a new Pay Rate Table or use an existing Pay Rate Table.

Create the following formula, in this example the formula is looking at the Union Pay Rate table.

REG RATE TABLE LOOKUP:

LOOKUP(Rate [PR Pay Rate Table],"UNION",JOIN(Union ID [PR Time], Union Local [PR Time],Union Class[PR Time] ))

If you would use this formula on a Regular Pay Type Pay ID, select this formula on the Formula field. When entering units to this Regular Pay, you'll see the rate after processing this check.

If you would use this formula on an Other Pay Type Pay ID, select the calculation method of Other Units. On the formula field select this formula from the list. You'll see the rate after processing this check.