a 30 isn't anywhere near the largest tyre you can run on a stock suzuki rim.
34 9.5 15 Swamper will go on a standard sierra rim.
A 9/34 16 Swamper will go on a 16" sierra/LJ rim
A Q 78 swamper will go on a 16X7" XL-7 or GV rim. That's 35.5 tall.
a 9.00 16 will go on a 7 rim easy, that's 36" tall.
Pretty sure you could run a 38X11 16 bogger on a GV rim too.
However, these are all cross ply tyres so aren't as rim width sensitive
A 30 X 9,5 isn't ideal on a sierra rim, but it's OK short term. It will likely crown a bit and the handling on road won't be as good as it could be. You will also have tyre clearance problems on the shock mount/inner guards unless you are WT.
Steve.