Yes, you can use the above method I mentioned for animating trees in your collection.
Growfx is quite cheap at $350, for what you get its a bargain in my opinion. Maxtree.org use it for all their libraries (and one of the best for plants IMO) so if you are buying their packs of trees you can get the bundle with growfx included for quick animations.
The way I look at it is, using 3dsmax to animate your trees is going to be painful and slow since you are working with a single cpu, animating high density geometry like this using modifiers etc will take so much of your time that by the end of your experiment you would have used more $$ in man hours than you could have if you just bought growfx and some maxtree packs, it also works with forestpro so you can combo these up for some great results. Just my 2c. Ive done it both ways, I ended up buying 4 licenses in total because of the value it gave our team.