Deunan has updated his Makaron blog again.

Okay people, here's what you need to have vibration:
*1) T9/3 or T9/4 Makaron executable
*2) T9/5 or T9/6 MakaronPAD.dll
*3) Maple.ini edited so that MakaronPAD is being loaded instead of MakaronVMU for Slot 1 or Slot 2 on given port
*4) Gamepad capable of vibration
*5) Game with PuruPuru Pack support (you might still need to enable it in game options)

If you can't get T9/4 to run at all with supplied Maple.ini (crashes with an 
error), but it does work if you modify it to have VMU (or nothing) instead of 
MakaronPAD in the Slot1/2, it's a problem with my code not doing the right 
thing with your pad. Another easy way to check is to use Maple.ini (and 
plugins too if nothing else helps) from T9/2.

If it does run but you get no FF effects it could be the game doesn't use it 
or needs to have it enabled first. If you're positive everything is as it 
should be, it's probably my code again. A fast way to test if the plugin is 
loaded as it should be:

HOLLY/Maple: 0x20: Makaron controller (0x00270101 / 0x00540905)
HOLLY/Maple: 0x01: Makaron VMU (0x00030201 / 0x00540904)
HOLLY/Maple: 0x02: Makaron controller (0x00270101 / 0x00540905)
HOLLY/Maple: 0x60: Makaron controller (0x00270101 / 0x00540905)
HOLLY/Maple: 0x41: Makaron VMU (0x00030201 / 0x00540904)
HOLLY/Maple: 0x42: Makaron VMU (0x00030201 / 0x00540904)

See, the 0x02 address of port A is using PAD plugin instead of VMU.
BTW, don't try to be too smart and have 2 VMUs and a PuruPuru Pack together.  
Though it's possible to assign addresses 0x04, 0x08 and 0x10, no real 
Dreamcast device has more then 2 slots and most games will not recognize such 
configuration. You can try your luck with homebrew KOS/Linux/BSD software, 
those usually don't have such limitations.
For those of you who never had a DC controller in their hands - PPP will fit 
in Slot 1 but it's big and will prevent you from using VMU in Slot 2. Not to 
mention only Slot 1 VMU LCD is visible (in Makaron too) so it's best to stick 
PPP into Slot 2.

And another thing - you'd be suprised how broken gamepad drivers can be. I've 
got two and each had it's nasty suprises (and I've yet to try PS2 Dualshock 
USB interface). Also, force feedback features can vary from very basic  
"rumble" ones to a real force working against your moves. It's not that simple 
to get those more complicated gamepads to do simple vibration it seems...

Source: dknute.livejournal.com