There is no 1:1 equivalent.
But the driver does round-robin scheduling of requests to units, and has per-unit rate limits. If, in a single poll rate, you have multiple requests to each of four units, they'll be executed like so:
- Unit 1 Req 1
- Unit 2 Req 1
- Unit 3 Req 1
- Unit 4 Req 1
- Unit 1 Req 2
- Unit 2 Req 2
- ....
If the each set of requests takes longer than the per-unit rate limit, then the poll will smoothly run through all of the requests from start to finish, then wait for the next poll start.
If the four units' requests are quicker than the rate limit, then there will be pauses and/or re-ordering inserted to fit the constraints.
Perhaps you should test with your application? (All of my non-free modules honor Ignition's two-hours-at-a-time trial mode.)